A red one
Seriously, need more info than what you have supplied.
what is the rest of your system for example, mobo, cpu, memory?
i have new pc which has.following:-
cooler master GX650 Watts psu
Asus M5A97 R2.0
Amd Fx 8120
Transcend 4 gb DDR3 1333Mhz ram
Western Digital Caviar Green 1TB HDD
Nvidia GeForce 8400GS.
iam planing to buy new graphic card to run assassins creed 3 .