The nvidia reference cooler is good. It’s pretty quiet for how good it cools, I don’t think it will be heard over the PSU fan. I know gigabyte makes a passively cooled heatpipe 6600GT model. I dunno if it cools good enough though. I’ve seen a couple other heatpipe cards, I think albatron makes one. MSI has a litle different cooler on theirs, and it’s supposed to be good too. I put a jetart jacsh1 heatsink on my 6600GT, and it’s really quiet. Plus it cools waaaayyy better than the stock heatsink, 50c load on the GPU. It’s only $20 for it, also sold as the logisys CF 206. I would avoid the newer XFX 6600GTs, they have some problems. Their new heatsink SUX too, and they don’t have temp monitoring now. Neither does MSI, but there’s a bios mod to fix that. I hear the gigabyte 6600GT is pretty good even with the fan. There aren’t a whole lot of bad ones, even a lot of the XFX ones are OK. Good luck, hope you find a good one.