Not sure if this is in your budget, but right now Newegg has 7950s on sale for ridiculously cheap prices. I just picked up 2 of these:

http://www.newegg.com/Product/Produc...82E16814202026

Thats a $300 card for $200 bucks(theres a $20 rebate). Even a single 7950 would be a monster of an upgrade over what you are running. However, I would recommend you make sure your power supply is up to the task.