Oh, that little Companion Cube. Maybe it's the little hearts on the sides or the way it's so perfectly weighted, but there's no denying it was the real star of Valve's mind-bender, Portal.
This particular cupboard was crafted by one James White and comes complete with cake (and, of course, a scrawled sign about the cake being a lie). If you fancy trying to make one yourself, he's offered up a ton of picture detailing the process on his blog, and in the comments he'll even give out the specifications.
This isn't the most useful cube we've seen today, but it sure is the cutest.