Here's my first Pendulum. It was built directly from the Junkbots, Bugbots, and Bots on Wheels book. It is self starting, simple, and cheap. The swinging magnet with the fishing line can be mounted just about anywhere and be almost any length. The base is where the magic happens!
Here's a little closer view of the base and electronics. For a circuit schematic, see my Circuits section. It works on back EMF generated by the coil when the magnet is close to it. The coils are from an old floppy disk drive and the electronics are from various pieces of "disposable" electronic devices. Total cost to build: free!! (except for the solar panel)