Dell Small Business has Dell PowerEdge T20 Tower Server System for $489 - $210 w/ coupon code 279T20 = $279. Shipping is free.

Note, if you have an American Express card then you may want to check your card to see if you have the offer explained in this post.  (Thanks zjs2k)

Specs

• Xeon E3-1225 v3 CPU
• 4GB DDR3
• 1TB HDD
• DVDRW
• No OS