'great' bookshelf speakers for under 500?

I've owned Soliloquy 5.0's and Ruark Epilogues, both available for under $500 used, and both are excellent monitors.

There is a fellow selling Silverline SR-11's used on Audiogon. Asking $675, retail new is $1500. Buy these and you will never look back - although at some point you'll probably add a REL sub, as you would for any high quality minimonitor.
Art

If you're talking about buying new, the KEF Q1 stand mounts would offer a smooth and somewhat warm sound, which is what you want in a budget speaker (to protect your ears from any fatigue associated with budget tradeoffs.)

It's been a while since I've heard them, but many years ago I owned a pair of Phase Tech PC-80's that were excellent. Since then, the PC-80 has been replaced by the PC1.1 and PC3.1. I believe the PC1.1 is around $500...

I loved my Totem Ones so the Dreamcatchers might be good. I would recommend the Quad 11L or Dynaudio Audience 42 in your price range (used). Pony up another $100 and look at Quad 12L, Dynaudio Audience 52, Green Mountain Europa or Von Scheikert vr1. These seem to be the most popular at this price point, well reviewed and hold resale value. This again is based on used price. The extra money should possibly buy you a little more bass extention and scale. Lots of nice little speakers out there that dont cost crazy money these days.