I used Philips' Luxeon Rebels in my light, and am very happy. They are available from futureelectronics.com, along with Polymer Optics lenses.
I think all the name brands are good, SSC, Cree, Luxeon, and some others. It's more a matter of which one has the size, layout, lens/reflector availability, etc. that fit your application.
There are a couple of important things to look at when comparing LEDs:
1. Physical outline. If you buy 'stars' they just screw down and you solder wires to them. But they are big. Most of the others need to be soldered to a circuit board.
2. Lens or reflector availability. Some are for specific LEDs, and some are much easier to use than others.
3. Color. Best penetration of clear water is from 'cool white', as this is kind of toward the blue end of the spectrum. Best color rendition is neutral white. I've heard that best in greenish northern waters is 'that pea green color', which I'm guessing is what the manufacturers call cyan.
4. Lumens per watt. This is a measure of how much light you get for each watt input. Numbers vary from 50 to 180 or higher.
5. Maximum power. This is maybe the hardest one to get a good handle on. LEDs, especially higher power ratings, require good thermal design to run reliably at the rated power. Your design has to be able to get rid of the heat without allowing the LED die to get hotter than 125C or so. The big problem is knowing if you have a good design. Unless you have fairly sophistocated engineering skills, you have to rely on the experience of others and/or your own seat-of-the-pants skills. Once you have it built, even if you don't push the limits of the power rating, a bad design may fail within hours, minutes or even seconds of being powered up.
