For $500, you should definitely put the Outlaw 1050 near the top of your list. Since Outlaw sells direct, via Internet, you avoid the middle-man markup and thus get a lot more product for your money (such as 6.1 channels, and decent power output). The Outlaw 1050 has gotten very good writeups, and won the 2001 Budget Component "Gold Award" from Stereophile Guide to Home Theater. For more info, here's the link to the Outlaw Web site (click on the "Products" icon on the left side of the page):
http://www.outlawaudio.com/rules.html