Evil Mad Scientist has another great tutorial on their website. This time it's an easy way to control high-power LED's. They came up with a simple circuit that uses a "blinking" bulb from a string of holiday lights instead of something like a 555 IC or micro-controller.
Read more about an Easy high-power LED blinking circuit
http://blog.makezine.com/archive/2008/06/easy_highpower_led_blinki.html