I've got a coralife 65G and it hasn't done me wrong.
I've heard people say to stay away from coralife, but so far so good over here. It measures right about 4" from the backside of the tank to the end of the unit, once hung. I got it at a LFS for $140 new, but I'm sure you can find them online cheaper. I just happened to be picking up a few things at the fish store and decided might as well grab it while I was there.