Nvidia 8800GT, aim for one with 512mb of memory. You will need a new PSU, 600W should do it make it modular if you can (only need to plug in the things you need, meaning less wires) Can pick them up for about £160 and they can overclock like mad to give mental results. 8800GT PSU That graphics card I linked takes up 2 slots at the back of the computer, make sure you have room like. The cooler takes up a seperate slot, but it will allow the card to run at lower temps. I have a gainward one, but the 1GB version and it runs at like 55 degrees full wack on Crysis...