Perpetual motion machines either produce more energy than is put into them or convert heat into other forms of energy without warming something cooler than the source of the heat. See http://en.wikipedia.org/wiki/Perpetual_motion_machine for a more detailed explanation.
The Bessler Wheel
Overview of a machine designed by Johann Bessler in 1712, that underwent numerous tests and passed rigorous inspections.
Flying Dutchman Projects
Collection with ideas and experiments in the search of a device powered by permanent magnets only.
Free Energy and Perpetual Motion
An account of Johann Bessler and his perpetual motion machine. Includes new theory on free energy machine, plus description of secret code, containing full details of construction of his machine - so far not deciphered.
Free Energy from a Collapsing Magnetic Field
Fuelless engines and generators, built and tested by inventor Rick Harrison. Creative Science and Research sells plans and kits.
Historical research and information on Johann Bessler, aka Orffyreus, and his demonstration of a series of claimed perpetual motion wheels in the early 1700's.