If you are a 1/2 way decent negotiator, you can jump from the Onkyo 600 to the Onkyo 700 for pretty much your price range.
I paid $619.00 (including sales tax) for the Onkyo 700 -- by showing Circuit City on-line prices and asking them to meet and/or come close to those prices.
You get more wattage as well as pre-outs with the 700.
RE: Onkyo SR600.......I was wrong.....it IS normally $499...I must have seen it for $399. :b
Eric_Strickl.....I am using an Onkyo TX-SR797 but just bought an Audiosource Amp One on ebay for my first dabble into separates....I'll probably be sorry (moneywise)! Or should I say my WIFE will probably be sorry!
h/k's are nice units in your price range as well in case you're able to try one out, the 325 fits in yoru price range and the 525Z does also i think. and you get multi room/7.1 capabilites