anything from nVidia gtx-560 and above or similar AMD/ATI
min 1gb of video ram
i am currently just using a ASUS GTX-460, and its doing a fine job, its now 2 gen old.
A 2 or more gigabytes of VRAM will let you have more textures in memory, if you are running large files. but a x60 is fine for most none gaming people