An anonymous poster criticized my use of LM317 chips as current regulators for high-power LEDs. While I think they are great for 350 mA single LEDs, they are clearly inappropriate for the 12 watt LED that I was playing with.
My LED was taking around 800 mA @ 12 volts. A little searching around reveals that a good alternative is the AP8803 which is a LED buck driver which can handle 1 amps @ 8-30 volts. The nice thing (aside from its 92% efficiency) is that you can set up a dimmer circuit on it using minimal parts -- or PWM control from a microcontroller.
For 350 mA LEDs, the AMC 7135 seems to be a popular choice although it's just a linear regulator, just like an LM317. Here's some AMC7135 driver hacking: http://www.candlepowerforums.com/vb/showthread.php?t=195358
and some hacking schematics: http://www.candlepowerforums.com/vb/showthread.php?t=216148
If you want ready-made LED drivers, this website has a good list of choices: http://www.videofoundry.co.nz/ianman/laboratory/research/driverlist.php
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