Hey O,
I'm asking myself a similar question. I was looking at a silent nvidia 8600 or 9600 cards, but I have been reading some reviews that although they perform really well, they run pretty hot, and they draw quite a lot of power even when relatively idle.
I've been looking at this review of the ati 3850 and 3870 cards which seem pretty good.
http://www.silentpcreview.com/article811-page1.html
The 3850 has a fan, but is apparently fairly quiet and draws little power.
Cheers
grog