I'd say that a radial fin HSF like the Zalman mentioned above would be the most effective that would fit in there. There are quite a few of that type out there like the Tt Orb models. The main problem with that case is height. I think you should have at least a 3" radius from the center of the CPU socket to the side of the case so the even the Zalman CNPS7700AlCu or Blue Orb would probably fit. A number of other brands also have radial fin HSFs like Masscool, Spire, Coolermaster, etc. Any of those should do you.
I normally buy either aluminum or aluminum with copper core - I don't think all copper is worth the extra weight and expense (when the current high copper cost gets to the channel). Of course any other low-pro design would work, they probably won't be as effective as a radial fin design though. Also avoid HSFs with custom fans that can't be replaced with a normal one in some way as all fans will eventually die. The zalman (thus probably the Orbs) can be replaced with a normal fan motor removed from its frame - there are articles on the web about it.
And the fins don't need to be anywhere near as long and fancy as the Zalman/Orb to be effective. Mine isn't much larger than the cpu socket itself.
.bh.