Thermalright HR-01 Passive CPU Cooler
 

The Thermalright HR-01 would be perfect for a HTPC, or any situation where you need your computer to be at its absolute quietest. With no fan on the HR-01, the processor cooler makes absolutely no noise. I was initially concerned that it would not be able to cool my Opteron 148 sufficiently, but in my tests I received a 10 degrees Celsius drop from the stock AMD CPU cooler.