90 gallon lighting

how deep is the tank?

i would go with 250's.. then you can put corals where ever you want!

That should be sufficient for what you want to keep. There is the potential that you'll want something more demanding down the line, so to accommodate that, I suggest 250w. Either that, or something like using the 175w Iwasaki 15000K lamp, which is extremely bright and is comparable to many 250w lamps, but with less energy. This is also something to consider given the height of the standard 90g tank. Just trying to keep your options more open, as most people invariably gravitate to other things at some point in time. Doing it now will save you a lot more money in the long run.

Edit: Ninja'd again, lol. I'm dropping the ball lately.

Should be 6 inches shorter. Again, the 150s will work for either application for the corals you want. It is just that if you end up looking at more demanding corals in the future, it would do you more good to look at the other recommendations to save time, money and frustration. If you know for a fact that you won't want to try out different corals and other photosynthetic organisms that are more demanding, then stick with the 150w. You'll just be more limited as to what you can keep and where you can keep it. You would be able to keep practically anything at the upper levels of the tank, however, the bottom is a different story.

I would do it once and get 2 250's. You will get different corals than what you want now. Its better to get the lighting that will support all corals then have to upgrade and spend the money all over again.

I have 1 MH over my 100long with some flourescants and I regret it everyday... I'd rather have two 175's and 2-4 T5HO's