Deal expires December 24th
The Alienware X51 Core i3-2120 desktop is only $649 until 12/24 after a $50 price cut from Dell. If you include a monitor, you'll add around $250-$300, but you can add the MG100 optical mouse and keyboard for free.
Although it comes with the 2nd generation Core i3-2120 3.3GHz processor (not Ivy Bridge), the Alienware X51 can still run the latest games. Backed with 6GB RAM and the NVIDIA GeForce GT640 1GB, this desktop should meet your needs for another couple years.