In general, I like the Cambridge Audio stuff for receivers/integrated amps (meaning, not separates). I've also had AMC stuff I've liked, particularly if you want tubes at a fairly good price.
Probably helpful to know what you're looking for. Receiver generally = integrated amp + tuner. Integrated amp = preamp (multiple inputs, volume control, tone control, balance, etc.) + power amp. Then there is the 2ch (audio) vs 5.1/6.1/7.1 stuff for home theater.
For $500 on the used market, you could probably get combo of separate preamp + power amp. Perhaps something like the Symphonies tube preamp + a solid state amp (Rotel, Hafler, AMC, etc). Unless you really want the space savings of an integrated, or want 5.1 for home theater, or want the tuner portion (i.e., your request for a receiver).
Lots of possibilities for $500 if you're talking used, but if you really only are interested in a receiver as your only option, that will obviously limit things.