Cult of Mac comes up with yet another classic re-use of an old Mac: they posted about this PowerMac G5 sidepanel that's been turned into an office space Nerf basketball backboard. The cardboard setup apparently broke down, so they replaced it with this Apple logo-labeled sidepanel from an old PowerMac G5 that had been turned into parts. Beautiful!
Of course you should always recycle any old Macs you aren't using any more, and Apple has an official program set up for just that. But I would rather reuse a computer for something like this: simple, functional, and pretty darn ingenious.