I know 6cm is nothing, but sometimes you have no choice its needed it for a barebone.
I was thinking about silentx but the complaint in the 12cm topic shocked me a bit, so i though lets look for other good fans. I was looking for nexus but could not find a 6cm.
Hmm, 60mm, tough choice. Most of the good 60mm units went out of production when they stopped manufacturing 60mm heatsinks for the old Socket 7/Socket 370/Socket A stuff.
Because of the small motors they die very easily and make a horrible sound at any decent airflow. Its a very high piitched thing.
I just bought a silenX 60mm highest airflow to replace a socket A fan. It was a little quieter but didn't cool the chip as good so I put the old one back. SilenX is a bit more expensive and the noise level might be hard to confirm, but I think they delivered what was promised.
Honestly, I'd cut out the 60mm hole, so there's no restriction, and put in a crappy socket A fan there... The AMD supplied ones really seem to be the... best...
I've got a Thermaltake 60mm from my old Thermalright SK-6 mounted on my IP35's pwm heatsink. Even turned down as far as my Kama Meter will take it, it's still as loud as 4 120mms and the 8800GTS put together.