As all the writeups thus far have been directed towards magnetic confinement fusion reactors, I feel I must mention the possibility of inertial confinement. Basically, you stick a fuel pellet in a target chamber and fire lasers or ion beams at it from all directions. The pressure from the beams both initiates fusion and confines the plasma. Neat, huh? Only thing is, most people (myself included) are convinced that this method is impractical for power generation, and that research in this vein is, rather, a weapons program. But hey, that's fine with me. I just think the NOVA laser is increfibly cool.