Vantec Iceberq (Copper)Those are what I have on my V5 5500 right now. They fit fine and look pretty nice, plus they don't don't block any other PCI slots. They're a little noisy, but not bad. I think you could slow them down a bit with a fan controller and still get adequate cooling (since the H/S is copper), but I haven't tried.
Before that, I was using Zalman NB32 passive heatsinks. They fit perfectly as well, but you need to make sure you get the newer model (with stepped clips), because the old version had crappy mounting clips.
The Zalmans looked GREAT, but you need a case fan blowing air over them for sufficient cooling. I had a nice quiet, low-RPM 120mm fan blowing air over the card from the end, and it worked fine.
There are pictures of my setup with the Zalman coolers
in this thread. I don't have any pictures of the card with the Vantec copper coolers.