Apple Mac Mini MC815LL/A Desktop PC for $568.95 shipped.  Here is a screenshot for your reference.  It features an Intel Core i5 processor at 2.3GHz, 2GB DDR3 RAM, 500GB hard drive, wireless 802.11a/b/g/n, Gigabit Ethernet, Thunderbolt port, FireWire port, Mac OS X Lion OS, and more.  Most places have it for about $599