You probally already know what I am going to say Keefe....water cool it! If you want to really reduce the amount of noise that is a good (but not exactly the cheapest) way to go. I like to keep the insides of my systems as clean as possible, I have never been to fond of the look of foam and what not inside of computers.

There is a company that makes a thin, aluminum foil looking sound and heat insulation for automobiles. If you are interested in it, you could probally find it on an automotive custom parts website or maybe a site that deals with car stereo products. I can't find the product in my old VW magazines, otherwise I would post the product info here for ya. You could line just about everything in your case with it, without it getting in the way to much.
Hey, I am actually plugging a product that we don't sell...go figure!