Some of the newer MTX amps are pretty small, and i never had a problem with mine other than them being stolen, and they can be had easily and cheaply. I've only had first hand experience with MTX and JL Audio's, so i can recommend them, but other than that you get into hearsay and subjective reviews. Unless you go really cheap most amps will foot the bill. You usually get what you pay for in amps, but unless you are an audiophile, there's a wall of diminishing returns that you'll run into pretty quickly. I think you'd be alright with an Alpine or MTX from your local Circuit City... or reasonably priced amps your local custom installer would have.

I see you're in SF... are you having them installed or are you doing it yourself? I think there were a few posts about places to avoid in SF if you're having them installed...