Turn your Kindle into a barebones computer.
Build an arcade table.
The Pi can run all sorts of old gaming emulators. By embedding a Pi-enabled display in a table and tricking it out with old arcade buttons, you've got a nostalgic piece of gaming hardware appealing to even the strictest gaming aesthetes.
An automatic dog treat dispenser!
This little box has a webcam so you can see when Rover is nearby and dispense kibble for him from anywhere in the world.
Coffee with a phone call.
By calling a phone number associated with the Raspberry Pi, it can remotely trigger the coffee machine to begin brewing.
These guys built a supercomputer.
Run it on the power of the sun.
Whatever you're using your Raspberry Pi for, you can trick it out with some solar panels to keep it green.
Anonymize your web traffic with a Tor proxy.
Here's a step-by-step guide on how to turn your Raspberry Pi into a dedicated Tor proxy. By bundling this thing with your Wi-Fi router, it will disperse your Internet traffic around the globe such that it can't be traced to you.
A computer in your hand.
This one's great. It's as if a Linux machine and a GameBoy Advance SP ran headfirst into each other. The battery lasts for 10 hours for long mobile computing sessions.
Build a time machine!
Obviously not a real time machine, but this series of LED displays is driven by a Raspberry Pi hidden inside. A must for Back to the Future fans.