[JAMF]

You'll need to add a monitor, so something like:

- an ASUS VW193DR Black 19" for $109 (1440x900)
NewEgg link

- an Acer G215HAbd-1 Black 21.5" for $119 (1920x1080)
NewEgg link

Another optional system for $550.01 after rebate:

Intel Core i3-540 Clarkdale 3.06GHz 4MB L3 Cache
ASUS P7H55-M LX
G.SKILL Ripjaws Series 4GB (2 x 2GB) 240-Pin DDR3 1333
COOLER MASTER HAF 912
COOLER MASTER eXtreme Power Plus 700W
G.SKILL Sniper Gaming Series 2.5" 60GB SATA II MLC Internal Solid State Drive (Model:FM-25S2S-60GBSR)
EVGA GeForce GTS 450 (Fermi) 1GB 128-bit GDDR5

NewEgg link

Will need a DVD drive and eventually a 320GB hard disk, but those are $17-$18 and under $45 respectively.