I have a 30" deep 300 and am thinking of going from 400 W MH to LEDs. I have been looking at the photon cannon from Ecoxotic (and Chinese built ones that are similar).
One of our local sponsors sells LED units that are just under 16" long by 8.5" wide and under 3" tall overall. They come with 6' power cord, long cable hanging kit and a switch to shutoff the whites so you can see the colors pop beyond neon!
They are built inside a black metal housing (looks sleek) and they contain 85 Blue 1 watt leds and 34 White 1 watt leds, 3 tiny quiet fans keep it all extrememly cool.
I have seen the unit on a 250, that is only 24" deep and it looks real nice. I have a mixed reef tank and wanted to get peoples opinion, from their actual experience with LEDs on tank this size. My main concern is enough PAR for my clams and SPS.