The four factors of LEDS are what current are they driven at, the spread they give, the amount of heat they produce for the heatsink area, and dimmability.
Im in the process of setting up a 2.5gal and I have gone with gu10 socket LED bulbs from china. There is a thread on a different forum about having more than a years success with them with correct PAR values and growing SPS. They are about $4.50 a piece and on my 2.5 gal Im using 3 on a 55g someone I remember was using 22 ($100). Also rapidled seems to be a good company I have some friends who are using their LEDS and are having success with them. But the reason we use LEDS is for efficiency and long bulb life which really has to do with HEAT and its dissipation. The bulbs I mentioned before are ALL in ONES so all you have to do is wire them into an extension cord parallel not series. Or check out the thread that jvdub20 mentioned as they have examples of larger arrays from china though I cannot attest to the quality of any of them. I would try to stay away from CREE if you can as it will save you alot of money, Epistar and Brightlux can work just as well for half the price or less as not everyone needs a Ferrari in the garage when Honda will work.