Any PCIE card will do. Just make sure to get something that does not require a lot of power... like a 7 series card or ati equiv, as you are only using a 300w psu. 9800 recommends a 400w+ psu

Me personally, I have an MSI 7800 GTx I got off eBay for $30.00 and I'm currently using it in my backup PC on a shitty stock PSU. Runs WoW, TF2, CSS just fine maxed out