I'd say something easy and peaceful.. the aggressive fish are nice but i hate when i add a fish only to watch it get beat up by another fish to the point that i either need to remove the fish or it will die.
I think something easy that is reef safe is your best bet...then later on down the road you have the option to switch it to reef without the hassle of catching the non-reef-safe fish.
Saltwater Fish: Marine Aquarium Fish for Saltwater Aquariums
live aquaria is a great place to research fish, it tells the minimum tank size, ease of care, aggression, and if they are reef safe or not.