Well, the Zalman is virtually silent. In fact when it's running I doubt you can hear it unless you move up really close to it. It uses a 92 mm fan (larger size means you can run at less RPM) and a funny system for latching it over the heatsink. The good thing about this system is that it isolates the vibrations of the fan from the rest of the case, so again, further reducing noise. It also comes with a rheostat for changing the fan speed of the included 92mm fan so you can hit that sweet spot of adequate cooling but quiet enough so you can actually think.
This little cathode light of mine, I'm gonna let it shine!