It's certainly a serious undertaking, but this how-to mod for turning an unused phone jack in your wall into a super-secret hidden data storage compartment is pretty awesome. You'll need to really get your hands dirty and know what you're doing for this one, but if you've got the chops it looks like a fun DIY project.

What you end up with is a hidden 4GB (or however large you want) USB drive that you can access by plugging in a custom phone-to-USB cord. So while it looks like you're just getting online with some old-school 56kbps action, you're actually accessing some data that no one will be able to find. Awesome!

Spyroforum, via Engadget