George was telling me about a lecture he watched on the web by Robert Bussard, an aging physicist (perhaps best known for designing the Bussard Ramjet) who recently came very close to a fusion power system which generates more power than is put into it.
His small company Energy Matter Conversion Corporation (EMC2!) was funded by the U.S. Navy until recently, and he and his colleagues did not discover the amount of success they had achieved until weeks after they were forced to shut down their lab.
The reactor is constructed using six rings assembled into a box. Each ring contains copper windings, allowing a magnetic containment field to be created when power is applied. Here's a concise story at Defense News that does a pretty good job of outlining the project and its uncertain future (it looks like the U.S. Dept. of Energy doesn't like competition).
If you really want some in-depth information, check out the paper by Bussard: The Advent of Clean Nuclear Fusion: Super-performance Space Power and Propulsion.