http://www.woot.com/

They change items every day - most of the time to lame stuff. But some days they have some pretty juicy deals. Today's 10/12/2009 deal, for $485 delivered, is a
1 Gateway LX6810-01 Core 2 Quad 2.33GHz, 8GB DDR2, 640GB HDD, DVDRW, HDMI, HD Tuner, Vista Home Prem

Not bad. Though the Vista option isn't appealing.