xyster
10 MW
The Radioshack 150-in-1 kits I played with as a kid didn't come with mosfets. This little applet, linked to from wikipedia, helped me to understand their operation a little better.
http://www-g.eng.cam.ac.uk/mmg/teaching/linearcircuits/mosfet.html
http://www-g.eng.cam.ac.uk/mmg/teaching/linearcircuits/mosfet.html