For my birthday I got a Stirling cycle engine from my mom. I've made a short video of it running. It is running on a cup of hot tap water and I put an ice cube on the top to help it run faster.
Video courtesy of Upload Video and Images - Putfile
If anyone is interested Howstuffworks.com has a good article on how they work. Here is how it basically works. The water heats the bottom plate causing the air to expand. The expanding air pushes on the work piston. Thats the small piston in the brass cylinder. As the work piston goes up it spins the crank shaft and that pushes the displacer down. Thats the big Styrofoam piston in the bottom. That forces the air to the top where it is cooled by the top plate and contracts. This pulls the work piston down spinning the crank shaft more. The displacer then moves up forcing the air to the hot side and it starts all over again. I bought my stirling engine from a guy in Germany. Their site has some other videos of stirling engines running.