Long version:
I'm running a Gigabyte Radeon 5750 Silent Cell. Works a treat...fanless.
I've also got a Gigabyte 5770(which was in my DAW at first) in another computer, and that's the most powerful fanless card out at the moment(as far as I'm aware). Problem was the 5770 was so heavy it was physically bending my motherboard's PCIe connector(P5Q-Deluxe), so I had to get the smaller 5750 for my DAW, and put the heavier one onto a newer motherboard(P7P55D-E LX) for one of my kids PC's. This MB doesn't bend from the weight at all.
Funnily enough I now have more fans(controlled by a Lamptron Touch fan controller), than I did before. Or in other words getting a fanless graphics card, hasn't resulted in a quieter case yet...as I've compensated with extra case fans..lol I guess I've got more control over those fans than I would with one onboard a graphics card, but still... ;)
Short version:
I've got a Gigabyte 5750 Silent Cell on the DAW and love it!