doubletwist has a clean interface and the new airsync feature is fantastic. i do like poweramp and cubed, but with the recent progress doubletwist has made i'm hoping people will recognize it appropriately.
All these good threads, can't remember if I voted, but the eq, and content power amp can play blows the rest out of the water. It is 5 bucks, but good things aren't free.
PowerAmp. I tried several but PowerAmp was the one that seems to solve the lock-up problems my Droid X had with the stock player after Froyo. It's equalizer and presets work nicely as well!