We all know about the passive cases (Hush Technologies and MCUBED HFX) which are very expensive. However, if you have enought space in your case you can drop a Cooler Master GeminII in there (http://wiki.team-mediaportal.com/HTPC_cooling).
I've got one in my OrigenAE H5 (http://www.origenae.com/en/htpc_h5.htm) which is as low profile as possible for a full hight case and it fits in with room to spare. (see attached photos).
This is a great heat sink, its cooling my Intel E6420 in passive mode without any problems. I have a passive graphics card in the box too (8500GT), which is running much hotter than the CPU.
Now I have my case down to just one 80mm fan in the PSU and will be looking at some passive external PSUs in the future
I've got one in my OrigenAE H5 (http://www.origenae.com/en/htpc_h5.htm) which is as low profile as possible for a full hight case and it fits in with room to spare. (see attached photos).
This is a great heat sink, its cooling my Intel E6420 in passive mode without any problems. I have a passive graphics card in the box too (8500GT), which is running much hotter than the CPU.
Now I have my case down to just one 80mm fan in the PSU and will be looking at some passive external PSUs in the future