I have used rapidled.com, ledgroupbuy.com they are both good. There is also a new comer modularled.ca which is canadian owned and operated. They seem to have a good product which doesn't need you to solder anything hence the word modular. I don't like soldering so if I wouldve known a little earlier my led wouldn't have been so ugly but they work fine.
check it out, I just did my biocube 29 and my buddys, let me tell you, both tanks look awesome.
btw I use cree XPE royal blue and XPG neutral white with dimming function. Dimming was pretty cool when I first got it, but now I don't use it anymore unless someone is over and I am trying to show off all the flourcent LPS.