HardwareSecrets tested several video cards to see which one provides the best performance/watt ratio in order for you to get a high score at Folding@Home and, at the same time, not going bankrupt with the increase in your electricity bill.
"We got so excited in participating in the Folding@Home project that we built as many high performance systems we could running both the SMP and GPU clients. We were very happy with the results until we received our first electricity bill: our energy consumption more than doubled - and we haven't even had our systems running 24/7 for 30 days! Since we still wanted to contribute as much as we can to Folding@Home, we decided to go in a quest to find out if there is a way to score lots of points at Folding@Home and, at the same time, not going bankrupt. We got all video cards we had available here in our lab to see which one provided the best performance/consumption ratio. "
Check it out over here. Overall the most efficient card is the GeForce GTX 260, and the GeForce 8800 GT is the most cost-efficient one.