If you haven’t already I found this thread very helpful when building my HTPC last year.
http://www.avsforum.com/avs-vb/showthread.php?t=940972Lots of info without even having to post and risk getting flamed.
If you want as quiet and effective as possible, water cooling is a fun project. Definitely the quietest solution and it is very effective if you buy good gear. Glowing blue or green water tubes gets you the ladies too.
This might also be fun but I think he already bought the case:
http://www.pugetsystems.com/submerged.php