If I were to build a mini-ITX computer, I would use the Cubitek Mini-Tank case for four reasons: 1) it can handle a full-sized power supply, 2) it has the width for a real pixel pushing video card like the nVidia GeForce GTX 580, 3) it has plenty of room for a large CPU cooler (or water cooling!), and 4) it looks as badass as a chibi AT-AT walker!
Unlike many mini-ITX cases, which focus on a smaller size for the HTPC (home theater personal computer) builder, Cubitek has combined the small and large in a case that is nearly as big as a micro-ATX case that gives lots of expansion options for the mini-ITX builder.
If you are not familiar with the mini-itx standard, there is a good description of its dimensions and development on Wikipedia here. Basically, mini-itx is a low-power motherboard that measures 17 x 17 cm square. Some manufacturers including Intel, Zotac, and Gigabyte build mini-itx boards that support desktop processors and dedicated video cards that connect via a PCI Express expansion slot.
Generally, mini-itx boards rely on smaller power supplies, because they require less power than their larger micro ATX and ATX siblings. However, a mini-itx board combined with a higher-end video card will more than likely need the additional power supplied by an ATX power supply.
For more details on the Cubitek Mini-Tank and other itx cases reviewed by Tom’s Hardware, go here: Cubitek Mini-Tank : DTX Lives! Four Double-Slot Cases For ITX Gaming Machines.