[KarmaKiller]

Here's a list for ya:

Motherboard: $58.75
http://www.dabs.com/productview.aspx...11143,48760000

CPU: $143.47
http://www.dabs.com/productview.aspx...ationKey=11147

RAM: $52.89
http://www.dabs.com/ProductView.aspx...1025&InMerch=1

GPU: $105.73
http://www.dabs.com/productview.aspx...ationKey=11137
* If you can go over budget a bit, go for this

PSU:$66.61
http://www.dabs.com/productview.aspx...avigationKey=0

Hard drive: $35.83
http://www.dabs.com/productview.aspx...ationKey=11154

HSF: $11.92
http://www.dabs.com/productview.aspx...ationKey=11258

DVD Burner: $19.70
http://www.dabs.com/productview.aspx...avigationKey=0

That puts the total right at 497 (your money). And all that's left to get is a case, which you can pick out one to your liking.
All in all, this is a very solid system. It will handle anything you throw at it fine.
How does that look?