The nMedia Icetank is not strictly for HTPC usage, but considering how quietly it can cool, it is perfect for that type of use.  It is fairly large, but designed to fit almost any processor type, which greatly helps during installation.  Drop by O2 for the full review.
“The nMedia Icetank started off well with an easy first mount and ended well with solid performance, easily competing with a recognized great in the world of air cooling. The size of the Icetank is smaller and lighter than some but it stills requires a little finesse when mounting in some motherboards. Being Socket 754/939/AM2/478/775 ready out of the box is also a nice touch that many cannot achieve, the Icetank does.”

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