As it turns out, this is the first rain team I've ever made and I'm proud to say it's been fairly successful. The main focus of this team is the offensive core between Keldeo and Virizion, which can be surprisingly devastating.
Politoed M @ Leftovers
Bold Nature 252 HP/252 Def/4 Speed
~ Perish Song
Seeing as this is a rain team Politoed is a must. What we have here is a standard physically defensive set with Max HP, Def, and the leftover EVs being invested in its speed. Scald serves as a solid offensive option with a nice 30% burn rate and the boost from rain gives it a bit of a punch. Toxic can potentially cripple various pokemon that may want to switch in on a predicted water type move such as Jellicent. Running Perish Song on Politoed has proved to be really helpful as it limits the time a potentially dangerous set sweeper(or particularly annoying wall) can stay in. Protect is there to scout the opponents reaction and it has decent synergy with Toxic and Perish Song.
G Aevis(Tornadus-T) M @ Expert Belt
Timid Nature 252 SpA/252 Speed/4 SpD
~ Focus Blast
Tornadus was always a big threat on rain teams and I'm pleased to say his Therian form is no different. What he lacks in raw power is made up for with his speed, utility, and the ever useful ability Regenerator. The nature and EVs are tailored to maximize his Speed and supplement his SpA, while the remaining EVs are placed in SpD. Expert Belt allows him to feign a choice item while giving him a little boost whenever he scores a super effective hit. Hurricane is a reliable STAB move under rain and is usually the main driving force for Tornadus-T. Focus Blast, while inaccurate, serves as a decently powered coverage move and has a good synergy with Hurricane. Taunt is used to cripple a special wall looking to absorb a Hurricane such as Blissey and Chansey. It can also aid in hindering a set up sweeper that thinks it can get a free boost on a predicted switch. U-turn rounds off this set by giving it the ability to scout and it mixes well with Regenerator.
Athle(Keldeo) @ Choice Specs
Timid Nature 252 SpA/252 Speed/4 SpD
~ Hydro Pump
~ Secret Sword
~ Hidden Power(Ghost)
~ Icy Wind
With Choice Specs equipped, Keldeo serves as a highly effective wall breaker and a great tool to combat sandstorm teams. The EVs are pretty standard for a Specs user, maximum investment in SpA and Speed. Rain boosted Hydro Pump allows it to rip through the majority of the OU metagame with ease. Even pokemon that resist it run a very real chance to be at least 2HKO'd(some of them are outright OHKO'd). Secret Sword acts as a reliable auxiliary STAB move and makes short work of Blissey, Ferrothorn, and the like. Hidden Power Ghost is mainly for Jellicent, which walls every other move on this set. Icy Wind is used as filler as Keldeo is unfortunately one of the few water types unable to use Ice Beam. The speed drop Icy Wind causes may occasionally come in handy though.
Vestige(Virizion) @ Life Orb/Lum Berry
Adamant Nature 252 Atk/252 Speed/4 SpD
~ Leaf Blade
~ Close Combat
~ Stone Edge
~ Swords Dance
Virizion serves as the sole set-up sweeper of this team and thanks to its naturally high SpD and resistances it also makes a good response to opposing rain teams. The nature and EVs are intended to maximize its attack, which actually allows Virizion to hit fairly hard even without a boost. This is particularly useful as it allows Virizion to OHKO the standard Tornadus-T and Thundurus-T with a LO boosted Stone Edge. Leaf Blade and Close Combat are reliable and fairly powerful STAB moves and SE is there to give me the option of hitting Tornadus/Thundurus and the occasional Gyarados harder than any of its other moves. Somewhat ironically, my only set-up sweeper functions more like a wall breaker than anything else, so I rarely have a need to set-up a SD.
Providence(Jirachi) @ Leftovers
Trait: Serene Grace
Careful Nature 252 HP/ 252 SpD/4 Speed
~ Iron Head
~ Body Slam
~ Stealth Rock
At some point during the creation of this team I figured that I needed some protection against Tornadus-T as well as something to set up hazards. The standard specially defensive Jirachi set fills this role perfectly as it can take anything that Tornadus-T can throw at it while also being able to reliably set up SR. It can also take on the Lati twins with ease and can support the team with Wishes coming off of its base 100 HP stat. Body Slam is for spreading paralysis and Iron Head provides STAB with a 60% flinch chance with Serene Grace. Pretty standard stuff here.
Genesect @ Choice Scarf
Naive Nature 252 SpA/252 Speed/ 4 Atk
~ Bug Buzz
~ Ice Beam
This is one of the best revenge killers I've used in a long time. It has fantastic coverage and its typing leaves it with only one weakness. What really makes Genesect shine is its ability, Download. A free boost to its SpA upon switching in only makes its job easier, while a boost to its Atk will make its STAB U-turn hit that much harder. Bug Buzz is a respectable STAB move and the chance to lower the targets SpD is always useful. Ice Beam can pick off various dragons such as Haxorus, Dragonite, etc and thunderbolt is there to complete the lauded "BoltBeam" combo. STAB U-turn allows Genesect to scout out the opponent's response to it and bring in a potential counter. Heavy investment in Speed and SpA is ideal for Genesect to effectively perform its duty, while a Naive nature is used in order to avoid hindering the damage output of U-turn.
Well there you have it, my first rain based team. Any feedback regarding this team will be appreciated.