This is a little trio that I put together to use for the Pokemon World Tournament in Pokemon Black 2.
Whimsicott @ Leftovers
Careful nature + Prankster ability
EV's: 252 HP / 252 SpD / 4 Atk
Oh boy, Whimsicott. When I first heard that this pathetic-looking thing was being used as a lead I had major doubts. So I try it out and I find that it's arguably the most fun to use Pokemon ever. Depending on what is sent out, I either use Leech Seed or Substitute first. Prankster ensures that I will move first with those moves (no Speed EV's needed!), so I always get the first turn outcome I want. Then if a Pokemon uses a status move (say Lucario uses Calm Mind), I counter with Encore and quickly switch to KO (Garchomp uses Earthquake). If they use an attacking move, Whimsicott is suprisingly bulky and replenishes health like crazy. Leech Seed whithers down a ton of health over time and Substitute buys me that time I need (not to mention Leftovers keeps me alive even longer). Whimsicott keeps bulkier things in check, like Hariyama and Wailord, that Garchomp and Scizor would struggle a bit with. U-turn is used to deal a tiny bit of extra damage when switching.
Garchomp @ Lum Berry
Jolly nature + Rough Skin ability
EV's: 252 Atk / 252 Spe / 4 HP
Garchomp is relatively simple. Switch in, maybe Swords Dance (while consuming a Leech Seed recovery), then sweep. Lum Berry is for Outrage/or any unwanted status conditions. Stone Edge is used for coverage against Flying types since my team struggles with those a bit. Outrage & Earthquake for STAB and coverage. His Jolly nature isn't as handy as I would have hoped and I'm thinking about switching it to Adamant. The most handy thing about Garchomp, besides his sweeping capabilities, is that he is a handy switch-in against Fire types that would otherwise cripple my team.
Scizor @ Focus Sash
Adamant nature + Technician ability
EV's: 252 HP / 252 Atk / 4 Def
Scizor works like a charm. When he switches in, all it takes is one Swords Dance for Bullet Punch to OHKO Brock's Tyranitar. Bullet Punch is my most reliable move but Bug Bite works on bulkier things more effectively. The priority difference is a major set back, but Scizor turns out to be pretty bulky himself and with Roost coverage, he's usually all set. He also is a handy switch-in against Ice types that would otherwise cripple my team. I feel that there would be an item that would be more effective with Scizor other than Focus Sash... Maybe a Choice Band/Scarf? Life Orb?