The Arctic Freezer, in Intel (Freezer 7) and AMD (Freezer 64) versions, seems to be reasonably well regarded as a quiet, effective cooler.
http://www.arctic-cooling.com/cpu2.php?idx=10&disc= - from their site, both quieter and better cooling than an AMD boxed cooler
You need to mount it with the fan blowing through the heatsink, toward a bottom intake PSU fan, or toward a rear extraction fan, to make best use of the unusual alignment, and using a front or side intake fan would also optimize the airflow.
Gets good reviews, fits the standard retention module - about the only thing that you can really fault it on, is it goes against the current trend for "multimount" heatsinks that fit almost every CPU you can name.
Not used one myself, but the "7" seems to be the favourite silent replacement for the stock HSF in my current machine.
