Ok here is what my tests show about lights. I have two tanks running right now with two different lights. One light (on my 55) is the TCP 5100K bulb that is shown on Melv's Reef. I like it, it grows Cheato like crazy but you can't really find it locally!. It has an internal reflector that works MUCH better then the stock reflectors on the clip on lights. The other tank (the 40 gal) was running the bulb that cameron posted. It was 5500K w/o an internal reflector, BIG DIFFERENCE! I am now running a 6500K bulb on the 40 with an internal reflector and it IS better then the 5500K w/o but not as good as the 5100K with. Does that make any sense?!?
So, if you can find it, go with an internal reflector AND 5100K, If you can't go with the internal reflector and the 6500K, if you still can not find them, go with the 5100K with a GOOD external reflector (like what George has put on his.)