Just thought I'd correct those who said you can't get a 8800GT on a mini-itx. You can. OK I wouldn't suggest that card, but I have had a HD4670 running on my Commell LV-677DC in my hoojum cubit.
It makes things a little warmer than the 21 degrees that my T2600 runs at, but it is possible and works well.
What I would suggest is you use an additional brick PSU unit for a card like this or make sure you are very happy with your PSU. Mine is a built-in to the board 120W and I was a little worried but it works.
Other case would be Nexus Psile but with both of these cases the GFX card must be short, single slot and not too power hungry.