I made an LED
fixture for a high-light planted 20H. I'm using ten 3W Cree XR-E LEDs on the tank and I can grow pretty much anything I want. There's more details on the build in the LED
link in my signature.
One of the beauties of LEDs is their penetrating power. LEDs put more PAR deeper into the water than other types of lights. For a reef tank, I'd look at a mix of 10,000K white and blue diodes. You'll have to keep the white LED
circuits separate from the blues. I've seen people learn expensive lessons by mixing them and having the fixture runaway and start popping LEDS like a string of firecrackers. Cree seems to be about the best brand, but there are others like Luxeon.