I remember seeing NeXTcube computers on their initial release in the 1990s, but somehow never heard of the Power Mac G4 Cube computers of 2001-ish.

Very cool looking and high spec in their day, but quite slow by today's standards, of course. Seems odd they somehow escaped my notice. Apparently there are people gutting them and building modern Mac Minis into the casings, just for the looks...

http://forums.macrumors.com/showthread.php?t=1410317&page=2