I've been using this offensive core that's a little bit counter-intuitive, but it actually works surprisingly well...Tyranideo?
Tyranitar @ Choice Band
Trait: Sand Stream
Adamant Nature (+Atk., -SpA.)
EV's: 180 HP, 252 Atk, 76 Spe
-Pursuit
-Stone Edge
-Crunch
-Superpower
Keldeo @ Choice Specs
Trait: Justified
Nature: Timid (+Spe, -Atk)
-Hydro Pump
-Surf
-Secret Sword
-Icy Wind
It's a pretty simple concept, really. Keldeo's main counters (Jellicent, Lati@s, Celebi) are very vulnerable to being checkmated by CB Pursuit T-tar. After those Pokes are gone, there is hardly anything that will enjoy eating specs Keldeo's dual stabs. The nuclear power of Specs Keldeo also helps you make rain teams tread a little more carefully around you. You still have to carry stuff that can beat Tentacruel, Amoonguss, etc., but the point is, this is a cool offensive combination and even without the rain Keldeo can be a very viable Pokemon (although I'm pretty sure a lot of people know that already).