The LED game is heating up fast & furious with new innovations & products appearing on a regular basis. There's really no easy answer. Check some of the links already provided, then search & read some more. I've found that some of the information I read only a few months ago has already been pre-empted by newer stuff.
The options LEDs have opened up are almost endless. Controllability is one of the major factors adding to the complexity of what you can do with different colour combinations. You really need to know what your ultimate goal is as to what you wish to keep in your system long term.
As far as DIY, many of the builds for the last few years have been heavy on the Cree 3 watt emitters. There are alternatives however, such as PAR 38 spotlights & MR16 form factor lamps normally used for task lighting in the home. I'm thinking it won't be too long before the Edison base, screw in LED lamps offered to replace your CFLs (which replaced your incandescents), will be powerful enough to consider using for a FOWLR or even soft/LPS coral tank.
I'm relatively close to completing a DIY using 10 watt multi-chip LEDs and very much like how this is working out. There are few of these types of builds around, but more & more folks are beginning to expand their horizons from the Cree 3 watt LEDs to other form factors. There's a chap on RC using the larger 50 watt & up multi-chip LEDs as well. Pretty amazing stuff.
Here's a link to my DIY thread:
http://www.canreef.com/vbulletin/showthread.php?t=82206