Politoed @ Choice Specs
EVs: 252 Sp. Atk, 252 HP, 4 Speed
-Hidden Power (Grass)
We've all seen this set, most of us have used it... Specs DrizzleToed, an excellent way to open any team. Rain boosted STAB Hydro Pump takes massive amounts of health off anything that doesn't resist it, and even quite a few things that do resist it. Ice Beam hits most of what Hydro Pump doesn't, with Hidden Power (Grass) for Gastrodon. Focus Blast lets him win weather wars with Tyranitar and Abomasnow.
Toxicroak @ Black Sludge
Trait: Dry Skin
EVs: 252 Attack, 252 HP, 4 Def
Typical Rain Toxicroak, abusing Dry Skin + Leftovers + Drain Punch for maximum survivability. Bulk Up makes him bulkier and boosts his already good offenses, while Drain Punch heals him and Sucker Punch gets perfect coverage alongside Drain Punch. Substitute eases predictions and blocks status, plus lets him stall out things like Ferrothorn and boost off them.
Metagross @ Life Orb
Trait: Clear Body
EVs: 252 Attack, 252 Speed, 4 HP
AgiliGross loves the rain, and I love AgiliGross. Q.E.D; I'm using AgiliGross. Agility boosts his rather poor Speed to a very respectable level, from which he can sweep. Meteor Mash is a powerful STAB with a chance to boost his already amazing Attack. Earthquake gets coverage on opposing Steel and Fire types, while Ice Punch hits Dragons, Landorus, and Gliscor hard.
Volcarona @ Life Orb
Trait: Flame Body
EVs: 252 Sp. Atk, 252 Speed, 4 HP
-Roost / Giga Drain
Volcarona is a great Sun counter, and finds a niche in my team with a 100% accurate Hurricane, STAB Bug Buzz, and Quiver Dance. Roost heals off Life Orb recoil as well as other damage, but I'm thinking of running Giga Drain to hit Water types and do more or less the same thing.
Tentacruel @ Leftovers
Trait: Rain Dish
EVs: 252 HP, 200 Defence, 56 Sp. Def
There's 3 spinners that are viable in the rain, and my spinner of choice is Tentacruel. While he lacks Starmie's sweeping prowess and some of Blastoise's bulk, the ability to set up Toxic Spikes is invaluable to my team. Scald also is fun for the chance to troll Burn some physical attacker or another. Protect can scout moves and gets a free turn of Rain Dish / Leftovers recovery.
Thundurus-T @ Choice Scarf
Trait: Volt Absorb
EVs: 252 Speed, 252 Sp. Atk, 4 HP
-Hidden Power (Ice)
Thundurus-T gives me an important Electric immunity, as well as a free Ground immunity, but that's relatively inconsequential to my team. Volt Switch lets him scout targets and hop to a counter, while Thunder lets him sweep late-game. Hidden Power (Ice) if I predict an incoming Gliscor trying to soak up a Volt Switch, or for revenging Dragons, and Focus Blast lets me lead with him against Tyranitar (and get KO'd by Stone Edge after it misses).
So that's it, enjoy the superstandard Rain team.