Specklefin (whitespotted) groupers don't require too large a tank, although I think the recommendation is a 75. You could go with a sixline soapfish...they're very pretty, aggressive. The only downside is that if they get really stressed out, they exude a toxin that can poison your tank...though they're not a high stress fish from my experience. Of course, I only had one for a day...it scared my harlequin tusk wrasse so badly that it jumped out of the tank and hit the top glass. So he got the boot. (I think that he was only so aggressive because he'd been housed for months with a *horrible* clown trigger and a notoriously vicious domino damsel) It was also housed with a zebra moray and the two of them made a wonderful pair...very cool looking. Too bad the fish was evil lol
Take a look at them, and if you're interested...I think that grouperhead has a/or some soapfish. I seem to remember him posting on them...you could ask him
I'm sure he'd know more about them than I do...I just know that they're pretty lol