I use a kenwood amp.

its not horrible, but its not top quality either. They're one of those bang for the buck brands.

If you don't want to buy sony or pioneer, but you don't have the money for JL audio or RF, I'd suggest kenwood.

but if you want it to sound really good, I'd suggest JL audio.

example: I had my kenwood amp (I can't remember the model number, but its a recent one, with the built in fan, 800w peak power, selectable mono or stereo) hooked up to my kicker comp vr 12" 4 ohm subs in a sealed box. It was loud.

then I hooked up my JL audio 300/2 amp to my subs. Just a shade under the loudness of the kenwood amp, but oh-so-fucking-clean. It just hits louder on lower frequencies, especially with rap or techno. Like a good amp should

but ultimately, I'd suggest going to a good stereo shop and judging for yourself. We all have different ears, and we all listen to different music.