Poison-types have never really been considered as "good," by upper tier standards, perhaps the most successful ones including Venusaur, Nidoking, Gengar, and Venomoth. But here in NU, Poison-types are actually quite decent, as they can absorb Toxic Spikes, they resist Fighting-type attacks, and more. Many Poison-types are underrated, especially in NU, but don't be fooled, as they can really tear up the tier if given the chance!
Arbok
Arbok has been shunned for the longest of times since its inception in RBY. However, BW has given it a lovely gift in the form of Coil, which raises its Attack, Defense, and Accuracy, all in one turn. Arbok has a fantastic STAB attack in Gunk Shot, who's accuracy becomes near perfect after a Coil boost. Arbok also has great coverage moves such as Earthquake for Rocks and Steels as well as Sucker Punch for those damn faster mons. All in all, Arbok has improved greatly, even if it is still stuck in NU...
Ariados
Ariados... is a terrible Pokemon, to say the least. Its stats are all bad, it really has no good coverage, and its only niche is Toxic Spikes, and even then, Garbodor is better at it, for the most part. Ariados unfortunately doesn't have much going for it. Sure, Sucker Punch and Shadow Sneak seem cool, but then you realize that they aren't STABed, and Ariados's Attack is shit. It can't even use Baton Pass anymore since it no longer passes the trapping effects of Spider Web. Don't use it... unless you wanna troll the fuck outta someone.
Beedrill
Beedrill is slightly better than Ariados, but only just. It has a higher Speed stat, and therefore can more easily set up Toxic Spikes. It also has access to Swords Dance, making it a legitimate threat, should it manage to set up. However, Beedrill is still pretty outclassed by things such as Ninjask, so I personally wouldn't use it, but I guess, to each his own lol
Dustox
If you really want a Quiver Dancer, use Butterfree. Or Masquerain. Or Mothim. Basically anything but this piece of crap.
Garbodor
Garbodor is actually one of the few decent Poison-types, as it has respectable bulk, access to both Spikes and Toxic Spikes, Explosion, and a few other options. It has terrible type coverage, but doesn't really need it when its only purpose is to set up entry hazards. One of the better Poison-types in NU.
Golbat
Golbat has amazing stats (well, not really, but amazing with Eviolite!); and its defenses are quite impressive after investment and the Eviolite boost. It has a decent Attack stat, a great Speed stat, even without investment, a great movepool with moves such as Taunt, Brave Bird, Super Fang, Roost, and more. Golbat also sports a 4x resistance to Fighting- and Grass-type moves, some of the more common attacking types in NU. It unfortunately has weaknesses to Ice-, Electric-, Psychic-, and Rock-type attacks, but its defenses and instant recovery really makes up for this slight flaw. Golbat is an excellent example of a good Poison-type in NU; he shan't disappoint!
Haunter
Although it is more known for its ghostly attributes, we must not forget that Haunter is part Poison-type. As such, it has a powerful STAB Sludge Bomb that, when combined with STAB Shadow Ball, hits the majority of the tier for neutral or super effective damage, bar those random Steel-types such as Bastiodon and Probopass. Haunter can very easily run Hidden Power Ground in Sludge Bomb's place in order to deal with them. Haunter is one of the few Poison-types with an immunity to Ground, thanks to its Levitate ability. It also boasts immunities to Normal and Fighting as well. Haunter is a great example of an excellent offensive Poison-type; it is quite common as well!
Muk
Muk is a surprisingly good Poison-type. It has excellent special bulk, and can remedy its lower Defense with Curse. Muk also has priority in the form of Shadow Sneak in order to deal with fast Psychic-types such as Mesprit and Kadabra. Muk has a great movepool, with access to the elemental punches, Gunk Shot, Brick Break, and more. It can also feasibly run a RestTalk set, though it isn't as good as the Curse set, or a SubPunch set. Muk is very underrated in NU, and should be used more.
Seviper
At first, Seviper looks like a pretty good mixed attacker with low Speed, but in actuality, it is simply a worse Arbok. Arbok has better moves, and despite not being able to go mixed like Seviper, has higher Speed and more utility. Seviper really shouldn't be used unless you really need a mixed Poison-type attacker.
Skuntank
Skuntank is actually one of the better Poison-types in NU, as it only has one weakness to Ground, courtesy of its secondary Dark typing. It is immune to Psychic-type attacks and resists Ghost, meaning that it can switch in with impunity and threaten a KO with Sucker Punch or Pursuit. It also has a decent Special Attack to fire off Fire Blasts to roast Steel-types thinking they can wall it. Skuntank is also pretty bulky, meaning that it can take hits and dish them back out, with some investment, of course.
Victreebel
Victreebel is a Grass-type, but also has a secondary Poison typing. It is one of the most fearsome sweepers in the sun, as Chlorophyll doubles its Speed. It has a great offensive movepool with things such as Sucker Punch, Leaf Blade, Weather Ball, and Sludge Bomb. After a Growth boost in the sun, it's pretty much gg from there... Not to mention Victreebel also gets Sleep Powder to incapacitate its otherwise troublesome opponents.
Vileplume
Although it shares its typing with Victreebel, Vileplume is more defensively oriented, based on its stats and movepool. It has decent bulk, and can take Fighting-type moves all day with the proper investment. It also has access to support moves such as Aromatherapy, Moonlight, and Sleep Powder, making it a good threat, and not useless against things that would normally wall it. However, if you are not in need of a defensive Grass-type, then Vileplume probably isn't a match for your team.
Weezing
Weezing is probably the best Poison-type in NU, thanks to its fantastic Defense and respectable offenses. It can easily cripple the opponent with Will-O-Wisp, phaze with Haze or Clear Smog, and roast Steel-types coming in to wall it with Fire Blast. It can also handle bulky waters to an extent, thanks to its access to Thunderbolt as well. It makes a great physical tank, and thanks to Levitate, only has one weakness: Psychic.
Whirlipede
Whirlipede is an interesting Pokemon, as all it can do is set up Spikes and Toxic Spikes, and then die. It has a useful 4x resistance to Grass- and Fighting-type moves, making it easier for it to find setup opportunities. Unfortunately, it has literally no offensive presence, making it easy set up bait for a lot of opponents. However, it is still quite useful, and is one of the few Pokemon in NU capable of setting up Toxic Spikes.
Alrighty, you've seen what I have to say, so discuss Poison-types and their roles in NU! :)

Arbok
Arbok has been shunned for the longest of times since its inception in RBY. However, BW has given it a lovely gift in the form of Coil, which raises its Attack, Defense, and Accuracy, all in one turn. Arbok has a fantastic STAB attack in Gunk Shot, who's accuracy becomes near perfect after a Coil boost. Arbok also has great coverage moves such as Earthquake for Rocks and Steels as well as Sucker Punch for those damn faster mons. All in all, Arbok has improved greatly, even if it is still stuck in NU...

Ariados
Ariados... is a terrible Pokemon, to say the least. Its stats are all bad, it really has no good coverage, and its only niche is Toxic Spikes, and even then, Garbodor is better at it, for the most part. Ariados unfortunately doesn't have much going for it. Sure, Sucker Punch and Shadow Sneak seem cool, but then you realize that they aren't STABed, and Ariados's Attack is shit. It can't even use Baton Pass anymore since it no longer passes the trapping effects of Spider Web. Don't use it... unless you wanna troll the fuck outta someone.

Beedrill
Beedrill is slightly better than Ariados, but only just. It has a higher Speed stat, and therefore can more easily set up Toxic Spikes. It also has access to Swords Dance, making it a legitimate threat, should it manage to set up. However, Beedrill is still pretty outclassed by things such as Ninjask, so I personally wouldn't use it, but I guess, to each his own lol

Dustox
If you really want a Quiver Dancer, use Butterfree. Or Masquerain. Or Mothim. Basically anything but this piece of crap.

Garbodor
Garbodor is actually one of the few decent Poison-types, as it has respectable bulk, access to both Spikes and Toxic Spikes, Explosion, and a few other options. It has terrible type coverage, but doesn't really need it when its only purpose is to set up entry hazards. One of the better Poison-types in NU.

Golbat
Golbat has amazing stats (well, not really, but amazing with Eviolite!); and its defenses are quite impressive after investment and the Eviolite boost. It has a decent Attack stat, a great Speed stat, even without investment, a great movepool with moves such as Taunt, Brave Bird, Super Fang, Roost, and more. Golbat also sports a 4x resistance to Fighting- and Grass-type moves, some of the more common attacking types in NU. It unfortunately has weaknesses to Ice-, Electric-, Psychic-, and Rock-type attacks, but its defenses and instant recovery really makes up for this slight flaw. Golbat is an excellent example of a good Poison-type in NU; he shan't disappoint!

Haunter
Although it is more known for its ghostly attributes, we must not forget that Haunter is part Poison-type. As such, it has a powerful STAB Sludge Bomb that, when combined with STAB Shadow Ball, hits the majority of the tier for neutral or super effective damage, bar those random Steel-types such as Bastiodon and Probopass. Haunter can very easily run Hidden Power Ground in Sludge Bomb's place in order to deal with them. Haunter is one of the few Poison-types with an immunity to Ground, thanks to its Levitate ability. It also boasts immunities to Normal and Fighting as well. Haunter is a great example of an excellent offensive Poison-type; it is quite common as well!

Muk
Muk is a surprisingly good Poison-type. It has excellent special bulk, and can remedy its lower Defense with Curse. Muk also has priority in the form of Shadow Sneak in order to deal with fast Psychic-types such as Mesprit and Kadabra. Muk has a great movepool, with access to the elemental punches, Gunk Shot, Brick Break, and more. It can also feasibly run a RestTalk set, though it isn't as good as the Curse set, or a SubPunch set. Muk is very underrated in NU, and should be used more.

Seviper
At first, Seviper looks like a pretty good mixed attacker with low Speed, but in actuality, it is simply a worse Arbok. Arbok has better moves, and despite not being able to go mixed like Seviper, has higher Speed and more utility. Seviper really shouldn't be used unless you really need a mixed Poison-type attacker.

Skuntank
Skuntank is actually one of the better Poison-types in NU, as it only has one weakness to Ground, courtesy of its secondary Dark typing. It is immune to Psychic-type attacks and resists Ghost, meaning that it can switch in with impunity and threaten a KO with Sucker Punch or Pursuit. It also has a decent Special Attack to fire off Fire Blasts to roast Steel-types thinking they can wall it. Skuntank is also pretty bulky, meaning that it can take hits and dish them back out, with some investment, of course.

Victreebel
Victreebel is a Grass-type, but also has a secondary Poison typing. It is one of the most fearsome sweepers in the sun, as Chlorophyll doubles its Speed. It has a great offensive movepool with things such as Sucker Punch, Leaf Blade, Weather Ball, and Sludge Bomb. After a Growth boost in the sun, it's pretty much gg from there... Not to mention Victreebel also gets Sleep Powder to incapacitate its otherwise troublesome opponents.

Vileplume
Although it shares its typing with Victreebel, Vileplume is more defensively oriented, based on its stats and movepool. It has decent bulk, and can take Fighting-type moves all day with the proper investment. It also has access to support moves such as Aromatherapy, Moonlight, and Sleep Powder, making it a good threat, and not useless against things that would normally wall it. However, if you are not in need of a defensive Grass-type, then Vileplume probably isn't a match for your team.

Weezing
Weezing is probably the best Poison-type in NU, thanks to its fantastic Defense and respectable offenses. It can easily cripple the opponent with Will-O-Wisp, phaze with Haze or Clear Smog, and roast Steel-types coming in to wall it with Fire Blast. It can also handle bulky waters to an extent, thanks to its access to Thunderbolt as well. It makes a great physical tank, and thanks to Levitate, only has one weakness: Psychic.

Whirlipede
Whirlipede is an interesting Pokemon, as all it can do is set up Spikes and Toxic Spikes, and then die. It has a useful 4x resistance to Grass- and Fighting-type moves, making it easier for it to find setup opportunities. Unfortunately, it has literally no offensive presence, making it easy set up bait for a lot of opponents. However, it is still quite useful, and is one of the few Pokemon in NU capable of setting up Toxic Spikes.
Alrighty, you've seen what I have to say, so discuss Poison-types and their roles in NU! :)