I was strolling around wired.com when i cam upon this article:
The robotics department over at the University of Pennsylvania has created a very early version of the Iron Giant. (a movie where a giant robot gets blown up and all the pieces start to come back together)
This little robot was made up of pieces that where each robots on their own. When the pieces where separated they would talk to each other, via signals and Infrared, to come up with the best solution to join back together into one bigger robot.
There are many different applications with this kind of technology, but the one that I think would be the coolest is a 21st century version of Rock 'em Sock 'em Robots; Kids can controls robots in real time to fight each other and the one that gets destroyed looses then reassembles itself for the next round. Now of course the technology is not nearly advanced enough for anything close to this, but it would be a neat thing to see further down the line of robotics.