High power LEDs are getting cheaper and cheaper, however the constant current drivers, to drive them are pretty expensive.
Here, I'll show you how to built a simple and cheap, yet very effective constant current source.
The image shows the constant current driver hooked up to a 1W white Luxeon LED.
EDIT: This LED driver supports PWM, which means that you can control the brightness of the LED(s). Those fancy and expensive drivers doesn't support that. I'll post some schematics and applications as soon as i have time.
Step 1: Get the Parts.
a LM317 Regulator.
a Resistor (see next step).
a Heatsink for the LM317 (you don't need one as big as mine, I just took one i had laying around).
some Luxeon, or other brands of high power LEDs (see next step too).
some Wire to hook it up.
it will be a good idea to use a heatsink for the LED as well.