The steampunk mac mini mod was great, but even it can't compare to the awesome powers of this Mac Mini Pro design by Hideo Takano. On the surface, he managed to hack a mini to look like a Mac Pro that measures only 3.28" wide by 7.8" tall by 6.5" deep. However, the upgrades don't stop there.
Takano also added a single USB port and a power button to the front as well as an enclosure that slides off to reveal the hard drive in all its glory. The good news is that there is a complete guide on how to build one yourself—but unless you are fluent in Japanese, you will probably need to rely on the pictures. [Mac Mod Lab via 123Macmini via Ars Technica]