Since Latias lacks a rain dance set in the analysis I thought I would write one since it is completely viable in my opinion. I know Cost was looking into this as well so I'd be grateful if he could add something should I have missed anything. Anyway, this is my first analysis so please feel free to critique, you can be as harsh as you want as long as you are fair in your reasoning. Hopefully it will be of a suitable standard.
STATUS: Finished!
http://www.smogon.com/dp/pokemon/latias
[SET]
name: Rain Dance
move 1: Rain Dance
move 2: Dragon Pulse
move 3: Surf
move 4: Recover / Wish
item: Damp Rock / Life Orb
ability: Levitate
nature: Timid
evs: 4 HP / 252 SpA / 252 Spe
[SET COMMENTS]
<p>Latias can fulfill a special role in Rain Dance teams because it can set up the rain and also take advantage of it with boosted Surfs. An Electric resistance allows Latias to switch in with relative ease against Pokemon like Choice Specs Jolteon taking a maximum of 32.12% from its Thunderbolt. Latias also takes an average of 96.88% from a 252 SpA Life Orb Jolteon's Thunderbolt + Shadow Ball + Stealth Rock damage, meaning it can, on average, switch in and set up Rain Dance without going down, a feat not too many other Rain Dance supporters can do. It has other useful resistances including Grass and Fighting as well as an immunity to Ground-type attacks, meaning it can take most attacks aimed at Kabutops, Qwilfish and other popular Rain Dance sweepers without too much trouble.</p>
<p>The rain is very useful to Latias as it allows it to be able to 2HKO the standard 248 HP Choice Band Scizor with Surf 100% of the time with Stealth Rock damage. This Scizor can 2HKO Latias with its STAB Bullet Punch though, so you should already have rain up, and you have to hit it on the switch in with Surf. With Life Orb however, Latias has an 83.83% chance to 2HKO Scizor with Surf and Stealth Rock damage even without the rain. Having Latias' most common threat out of the way allows it to deal plenty of damage thanks to the great coverage provided by Water-type and Dragon-type moves, a combination only resisted by Empoleon and Shedinja.</p>
<p>Recover is the recommended move in the last slot as instant recovery means it can survive longer. However, with Life Orb recoil that your Rain Dance sweepers pick up, Wish could prove the better option in some cases to help your damaged sweepers. It may seem pointless having both Kingdra and Latias on the same team, but Latias functions a bit differently from Kingdra due to its access to an instant recovery move, having different resistances and higher Special Defense. This makes it a better supporter than Kingdra, who is better utilized having a more offensive role. Other options for this set include Safeguard and Thunder; Safeguard could be useful because it prevents paralysis, one of Rain Dance teams' greatest enemies, from crippling fast sweepers. Without the ability to inflict status, Pokemon such as Celebi, Breloom and Rotom-A become less dangerous to your team. Thunder is considered overshadowed by Surf, however it does hit bulky Water-types such as Vaporeon and Suicune harder than any other option meaning you don't have to rely as much on Ludicolo.</p>
<p>A Timid nature gives Latias that extra bit of speed that can come in handy when facing threats like Salamence, who often threatens Rain Dance teams. Damp Rock is the preferred item because of the extra turns of rain that it provides, meaning you don't have to switch as often to set up the rain again. It also means Latias can abuse its boosted Surf longer. Damp Rock isn't the only viable item for this set; Life Orb is a great alternative, because with it, Latias can 2HKO a max HP Tyranitar after Stealth Rock damage. It also scores a OHKO on a 176 HP Tyranitar while it is raining with Stealth Rock damage. Few Rain Dance supporters have the ability to 2HKO both Scizor and Tyranitar which makes Latias a worthy addition to any Rain Dance team.</p>
<p>This Latias fits best in a Rain Dance team that also has a Steel-type Pokemon such as Bronzong, Jirachi or Scizor who can soak up the Dragon- and Ice-type attacks which Latias attracts and possibly set up Stealth Rock as well, while Latias can take any Fire-, Ground-, and Fighting-type attacks that come their way. Since Latias can lure in Scizor and 2HKO it with Surf as it switches in, Kabutops can make a great partner, no longer fearing that dreaded Bullet Punch which haunts its existence. Qwilfish appreciates Latias switching into Ground-, Psychic-, and Electric-type attacks directed at it. Skarmory and Forretress aren't going to appreciate rain-boosted Surfs, and Salamence will not want to stay in fearing a STAB Dragon Pulse. Magnezone is another great partner for Latias since Latias lures in Choice Scarf Jirachi, Scizor, etc allowing Magnezone to switch in with ease and trap them. Magnezone can also set up the rain itself and possibly Dual Screens as well allowing Pokemon like Dragon Dance Kingdra, Swords Dance Kabutops and Swords Dance Qwilifish to set up easier.</p>
STATUS: Finished!

http://www.smogon.com/dp/pokemon/latias
[SET]
name: Rain Dance
move 1: Rain Dance
move 2: Dragon Pulse
move 3: Surf
move 4: Recover / Wish
item: Damp Rock / Life Orb
ability: Levitate
nature: Timid
evs: 4 HP / 252 SpA / 252 Spe
[SET COMMENTS]
<p>Latias can fulfill a special role in Rain Dance teams because it can set up the rain and also take advantage of it with boosted Surfs. An Electric resistance allows Latias to switch in with relative ease against Pokemon like Choice Specs Jolteon taking a maximum of 32.12% from its Thunderbolt. Latias also takes an average of 96.88% from a 252 SpA Life Orb Jolteon's Thunderbolt + Shadow Ball + Stealth Rock damage, meaning it can, on average, switch in and set up Rain Dance without going down, a feat not too many other Rain Dance supporters can do. It has other useful resistances including Grass and Fighting as well as an immunity to Ground-type attacks, meaning it can take most attacks aimed at Kabutops, Qwilfish and other popular Rain Dance sweepers without too much trouble.</p>
<p>The rain is very useful to Latias as it allows it to be able to 2HKO the standard 248 HP Choice Band Scizor with Surf 100% of the time with Stealth Rock damage. This Scizor can 2HKO Latias with its STAB Bullet Punch though, so you should already have rain up, and you have to hit it on the switch in with Surf. With Life Orb however, Latias has an 83.83% chance to 2HKO Scizor with Surf and Stealth Rock damage even without the rain. Having Latias' most common threat out of the way allows it to deal plenty of damage thanks to the great coverage provided by Water-type and Dragon-type moves, a combination only resisted by Empoleon and Shedinja.</p>
<p>Recover is the recommended move in the last slot as instant recovery means it can survive longer. However, with Life Orb recoil that your Rain Dance sweepers pick up, Wish could prove the better option in some cases to help your damaged sweepers. It may seem pointless having both Kingdra and Latias on the same team, but Latias functions a bit differently from Kingdra due to its access to an instant recovery move, having different resistances and higher Special Defense. This makes it a better supporter than Kingdra, who is better utilized having a more offensive role. Other options for this set include Safeguard and Thunder; Safeguard could be useful because it prevents paralysis, one of Rain Dance teams' greatest enemies, from crippling fast sweepers. Without the ability to inflict status, Pokemon such as Celebi, Breloom and Rotom-A become less dangerous to your team. Thunder is considered overshadowed by Surf, however it does hit bulky Water-types such as Vaporeon and Suicune harder than any other option meaning you don't have to rely as much on Ludicolo.</p>
<p>A Timid nature gives Latias that extra bit of speed that can come in handy when facing threats like Salamence, who often threatens Rain Dance teams. Damp Rock is the preferred item because of the extra turns of rain that it provides, meaning you don't have to switch as often to set up the rain again. It also means Latias can abuse its boosted Surf longer. Damp Rock isn't the only viable item for this set; Life Orb is a great alternative, because with it, Latias can 2HKO a max HP Tyranitar after Stealth Rock damage. It also scores a OHKO on a 176 HP Tyranitar while it is raining with Stealth Rock damage. Few Rain Dance supporters have the ability to 2HKO both Scizor and Tyranitar which makes Latias a worthy addition to any Rain Dance team.</p>
<p>This Latias fits best in a Rain Dance team that also has a Steel-type Pokemon such as Bronzong, Jirachi or Scizor who can soak up the Dragon- and Ice-type attacks which Latias attracts and possibly set up Stealth Rock as well, while Latias can take any Fire-, Ground-, and Fighting-type attacks that come their way. Since Latias can lure in Scizor and 2HKO it with Surf as it switches in, Kabutops can make a great partner, no longer fearing that dreaded Bullet Punch which haunts its existence. Qwilfish appreciates Latias switching into Ground-, Psychic-, and Electric-type attacks directed at it. Skarmory and Forretress aren't going to appreciate rain-boosted Surfs, and Salamence will not want to stay in fearing a STAB Dragon Pulse. Magnezone is another great partner for Latias since Latias lures in Choice Scarf Jirachi, Scizor, etc allowing Magnezone to switch in with ease and trap them. Magnezone can also set up the rain itself and possibly Dual Screens as well allowing Pokemon like Dragon Dance Kingdra, Swords Dance Kabutops and Swords Dance Qwilifish to set up easier.</p>