Hi BB
The Zalman range are very good at reducing noise ... have a look
HEREAlso you can look at the Papst fans
HEREThe Thermaltake Smart Case Fan 2 is quite good too, although I use it on the heatsink with the thermal sensor between CPU and sink ... when its not under load the fan speed is reduced thus reducing the noise
HEREYou may wish to consider a 120mm fan as opposed to 80mm as these can shift a lot of air, and if you have a speed controller, you can turn the spped of the fan down, and hence the noise, but still have the equivalent air-flow of an 80mm fan but with a lot less noise
You should find what you want