You might try the Arctic Cooling Accelero S1. It's got good reviews (see Google), and fits the 7950GT. It's only $18.99 plus shipping at SVC.com. It's a totally passive solution, so no noise at all.
If you need to cool it more (overclocked,etc.), AC has a virtually silent "Turbo" module for the S1. Or you could just point a quiet case fan at it, for that matter.