The Junk Box Switcher power supply
I built a PCB for a simple switching power supply, originally designed by Keith Payea of the SRS. It uses an LM393, a P-channel power MOSFET, and darn little else. Since its frequency varies based on load (and nearly everything else imaginable), you can use junk-box parts and build it for cheap. Here is the schematic (PostScript). See September 1995 in the article index.