Well not an entirely fair poll, because I'm about to upgrade - well I need the Nv45 to come out first but that's 6 mo away
I would have used fancier cooling, but on stock I got a 5950 to 565/1020, from the stock 475/1000, so I kind of stopped. Xbit labs used volt mod and super chilling to only get this chip at about 600 so there wasn't much need. And the stock cooling is silent compared to the rest of my system. There is an 80mm fan blowing on the card, Panaflo M series, but that's it. Stock though is the rather nice thin fin alum hs, with the air being pulled in from the outside over it, so its really no wonder it works so well.
NV40 and 45 are going to generate a more moderately serious amount of heat. I'm going Swiftech MCW50-T, pelt, on that one. 40 due Apr 13, 45 due July-Aug.
$.02