Ive seen a few very large car radiators that have copper tubbing and aluminum fins. Problem is they were all the kind that has tons of bends and is virtually just one really long tube so flow would be pretty crappy and Ive only seen 2 or 3 on ebay. Like the one this guy used but copper tubing:
http://www.silentpcreview.com/article171-page1.html
This would be the most practical as you could do what he did and attach it to the side of your case.
I think it was overclockers.com that had a guy using some sort of radiator that was used in something like a water heater or furnace or something
just something that some people have in their basement I really dont remember.
But it looked like a 1 inch dia. copper pipe that was 8 feet long with hundreds of square aluminum fins brazed onto it.
Naturally he ran it passive. Sorry but for the life of me I cant remember what its intended use was...
This isnt very practical though as he had to put it in some closet to just hold it up.