I've been very impressed with Danny's Rubik's Cube solver, both the mechanics and the programming (both of which I might add are beyond my usual range of experience). I recently came across another version by Hans Andersson of an NXT-based Rubik's solver, but one that is completely standalone - no PC or even image processing is required, and the parts list looks to be well under one NXT kit. It uses the US sensor to detect when a cube is placed in the cradle, and then scans it using nothing more exotic than the stock light sensor (he has used a specially colored cube to make the colors easily distinguished). Take a look at the YouTube video - in particular, watch the multi-jointed motion of the arm, (it seems to be a very nicely designed mechanism), as well as the simple way the scanning is accomplished. Not to mention the fun sounds it uses while calculating a solution. I'd love some more details on this project but I don't have any...yet. I am guessing he's used NXC with Bricx Command Center, as they are listed on his links page. Visit his site - it's brief, but well-written.
Han's Tilted Twister website: http://tiltedtwister.com/