$20 after MIR - XFX HD-645X-YNH2 Radeon HD 6450 512MB 32-bit DDR3 PCI Express 2.1 x16 - http://www.newegg.com/Product/Product.aspx?Item=N82E16814150581
If you want a little more power and are willing to come up a little in budget, I would get this:
$50 after MIR - XFX GT-430X-CAF2 GeForce GT 430 (Fermi) 2GB 64-bit DDR3 PCI Express 2.0 - http://www.newegg.com/Product/Product.aspx?Item=N82E16814150578
You will actually be able to play newer games on the GT 430. Plus, it comes with a free copy of Call of Duty 4.