Politoed, the 2nd king of rain and the starter of the weather wars in Generation V. Sadly its position has been usurped by Pelipper of all things, but Politoed has been around for a long time and still has several tricks up its sleeve.
A Froggy Rain
Politoed
Ability: Drizzle
Item: Damp Rock/Leftovers
-Scald
-Encore
-Hypnosis
-Toxic/Rain Dance
Nature: Bold (+DEF, -ATK) or Calm (+SDEF, -ATK)
EVs: 252 HP/252 DEF/4 SDEF
This Politoed is rather passive, but its purpose is to setup rain and hamper the opponent with statuses. Scald gets STAB, prevents from being taunt bait and enables Politoed to spread burns. Encore more or less enables safe switches for Politoed by guaranteeing what your opponent will be doing next turn down to the move they just used or switching. Hypnosis can take out a serious threat but its accuracy is crud. Toxic can cripple anything too bulky, while Rain Dance allows Politoed to get a leg up on other weather setters if you need Rain that badly.
Damp Rock is heavily recommended as Politoed can't get Rain Sweepers as quickly or safely as Pelipper, and Politoed's strategies being more time consuming/risky. Leftovers is for Bulk. Nature and EVs are for bulk.
Other Options
Icy Wind (doubles) -Speed Control is always nice.
Endeavor -Good surprise to cripple opponents when at low health, though requires prediction due to Politoed's low speed.