Finished Black 2 some two weeks ago with the following team:
Arcanine - I braced myself for some painful grinding, but surprisingly enough Growlithe really managed to hold it's own weight. My final set was Flamethrower / Outrage / Dig / Flare Blitz, but looking back, it is really more beneficial to evolve it right after getting Flamethrower, and sticking to Flamethrower / Dig / Crunch / Thunder Fang (or Dragon Pulse if you're willing to spend some shards) for your final set. Moveset aside, it has near-legendary stats after evolution and Intimidate is just godly (also helps with annoying encounters should you run out of Repels). Mid / High-Mid tier for me.
Scrafty - this guy has been beaten to death already, but let me repeat. Amazing bulk. Dark/Fight STAB. Moxie. High Jump Kick. Crunch. And now Ice Punch for even better coverage and Drain Punch for secondary non-miss Fight STAB. Top tier easily.
Lilligant (traded one) - one of the best in-game Pokemon I have ever used. Great utility mon (Sleep Powder) and major powerhouse in one. Black 2 Petilil comes early, has an experience boost due to a different OT, and on top of that, a freaking Timid nature AND Own Tempo. It's coverage isn't an issue when you assravage everything in your path with a well placed Petal Dance. Top tier.
Sigilyph - pretty solid mon all-around. Fast, pretty powerful, relatively bulky. I wished it learned Air Slash and Psychic a bit earlier, since Psybeam and Air Cutter slow it down midgame. Shadow Ball or Signal Beam are good for coverage. Also great utility in Fly. High-Mid tier.
Cinccino (Technician) - I was hyped to use this thing after hearing so many good things about it in BW1 in-game tier list thread, and needless to say, it didn't disappoint. Return/Wake Up Slap/Bullet Seed/Rock Blast just flips everything's shit inside-out, period. It didn't have a single slow-down period, which is great too. Best Normal type this generation, right next to Lilipup. High tier, possibly even Top.
Seviper - I'm not going to lie, I included it because the one it the trailer just looked so freaking cool (dat hiss) (Arcanine too). I expected it to be shitty, but it came out better than I expected. Glare is a major boon to this mon usability, as it fixes it's speed issue and hits everything for almost guaranteed paralysis. You can teach it Venoshock for an early STAB move, and replace it with Poison Jab as you level-up. Those two, along with Dig and Night Slash, give you a decent freshman set. The moment it really starts to shine comes with Coil which, in combination with Shed Skin and Black Sludge, allows for some awesome sweeps. However, below avarage stats really hinder it's potential, as do the absolutely massive amounts of experience needed to level it up. Another downside comes from the fact that, aside from the early Venoshock, you don't really get the chance to use it's great Special Attack, which more-or-less forces you to use the physical set (Flamethrower comes too late, while Sludge Bomb is postgame). All things considered, I would place this one in Low-Mid.