Interesting, this 1156 itx isn't plagued with the same issue as all of the other ones where a heatsink will block the PCI-E slot. Instead you may block the RAM like the LGA775 style.
In any case, I have the Gigabyte H55N-USB3. I've done some of the heatsink research. In order for me to not block the PCI-E slots the only 2 heatsink I could uses were:
Prolimatech Samuel 17http://www.prolimatech.com/en/products/detail.asp?id=157&page=1
] (check out the clearance)
The AXP-140 will give you the best temps out of all the choices. Great clearance for tall ram heatsinks (my G. Skill Sniper & Ripjaws fit under it just fine, but you have to install the ram first). But it is also the biggest and you have to use a thin fan in order to fit the Sugo SG05.
The Samuel 17 has a really good height clearance and you can mount a full 120mm fan and get some airflow to the rest of the motherboard. Also it will have clearance for ram if you use low profile heat sinks. Downfall is that it doesn't perform that well in something with high heat output like an i7. It cools a little better than stock and it's quieter because you can pick a better fan. It's also expensive for something that doesn't perform that well.http://hardforum.com/showpost.php?p=1036290331&postcount=174
Also if you look at the link above, they used a Big Shuriken on the same Gigabyte H55N-USB3. It does have clearance for RAM as long as the heat sinks are not too tall. So you should still be able to fit a full GPU on the board.
Looks like your limiting factor is the heat sinks on the RAM. Just make sure you have low profile ones and you should be just fine with all of these heatsinks. Good luck! Edited by RagingInferno - 4/7/11 at 12:09pm