This deal has ended.
Dell has their Vostro 200 Desktop for only $449 through 11/10. This is well-configured enough for most people and relatively inexpensive to upgrade. It comes with a 2.2GHz Intel Core 2 Duo processor, 1GB memory, 160GB hard drive, CD / DVD burner, Windows XP or Vista, and a 19" flat-panel LCD monitor. Shipping is free.