Brian (or Allan?) of HelloSimplyMusic answered your question above. The best amp for $500 or under is the Muse 100. I have a '92 model in my second system. I have auditioned lots of others. Except for the larger Muse 160, nothing else in the under $2000 new bracket was really acceptable. I haven't heard the Rotels mentioned above. They might be ok.
Best used amp for around 500
I'm am desperately trying to upgrade from a Denon AVR-3300 receiver. Looking for a stereo amp for the fronts. I'm entertaining the idea of a five channel amp, but I don't yet have DVD-Audio or SACD, and money is an issue. The receiver is fine for movies, but for music...well, it won't do. I'm currently running Acoustic Energy Aegis 3's for the fronts - silk dome tweets, pretty warm, laid back sound. Any suggestions?