With some help from the R2 Builders Club, my wife and I built an R2-D2! He drives, makes sounds, and lights up, but there's still a lot to do. For example, we haven't hooked up all the motors inside the dome and the motor to make the dome spin.
Here's some of the electronics:
Here's our R2 with a few friends:
We also built a prototype out of K'NEX: