I have some purple encrusting monti that is killer fast.... I got it about 2 weeks ago and it's already doubled. In another two weeks it'll have covered the frag plug and some of the rock, too-- and that's in the middle of an inadvertant ammonia spike in my tank.
As for LPS, my duncans are super fast and fairly hardy. Also, for a fairly fast growth but also cool factor, I like frogspawn. Mine's easly double what it was 3-4 months ago.
softies-- zoa's grow so fast in my tank. I blink and they've put out babies.