Well, the Playstation 3, of course! IBM has a fascinating series of articles on setting up the Playstation 3 for Linux development with the Cell Broadband Engine:

• Part 1: More than a toy - Describes the virtualized environment that Linux is given to run in on the PS3
• Part 2: Working with memory - Explains the setup of a usable environment that doesn't use nearly as much memory as the default install.
• Part 3: Slimming down X11 with tiny tools - Other ways to reduce the footprint of X11 on the PS3

Looking at this almost makes me want to try development on the PS3. But there are just too many projects for the available time...