Dell is your best bet for the $500 mark. There really isn't anything else with anywhere near a quality mark for that range. Beware though Dell will sting you for upgrades, things like a 3.5" Floppy can add up to $100!
The best low price I can sell, though my own business is an Acer Aspire AS80 for $500 shipped direct to your door.
Specs:
2.88GHz Celeron ; 256MB RAM ; 80GB HDD ; CD-RW/DVD ; 10/100MB NIC ; Windows XP Home Edition (English)
No Monitor, floppy add $10
BTW, this isn't me trying to sell my wares, but will give you an idea of what to look at, and it's my base unit. Acer are very competitively priced.
