Taking a break from the Kinect side of homebrew, here's the result of one project we're pretty impressed with. It's called the CCube (stands for Compact Cube) and as you might guess, it's a handheld GameCube mod.
We see these sorts of GameCube remakes all the time, since the original hardware so unbelievably compact in the first place, but they tend to be rather large and questionably portable.
Admittedly, this isn't portable either considering the lack of an internal battery means you require a power cable to work it, but size-wise it's quite an achievement. It's for sale, too (if you haven't spent all your cash on Nintendo's slightly better-made new portable).
Check out the video, and head over to the Mod Retro Forums for more on the project.