Antec is taking the idea of a bare-bones PC to a whole 'nother level with its upcoming Antec Skeleton open-air PC case. It won't wall in your parts like a normal PC tower, which can improve airflow (or, at least, provide more airflow from less fans if intelligently placed). It's the kind of case modders have been building on their own for years. The Skeleton's got a smaller 92 millimeter fan to cool the lower deck, and a honking, three-speed 250 millimeter fan up top. Despite it's looks, it's actually pretty big, too: It's a little over a foot in length, width and depth.
The Skeleton will give you plenty of room to work with, with four drive bays and seven expansion slots that can fit even the larger video cards, and the frame's made with 0.8 millimeter steel and reinforced with hard plastic. No price or release date yet, but it shouldn't be too long now that it's announced.