[Myka]

An Orchid Dotty, or if you want something more unique an Assessor. Any of the Cardinals would be happy in there. Clownfish would also be a good choice...any of the smaller ones (True Percs, False Percs, Skunks, Sebaes. All of the previous mentioned fish will do a good job of swimming all over the place. Jawfish would be a good choice, but stick to their burrow. Gobies would also do well, but most stick close to the sand. I would hesitate on adding any of the Firefish as they seem to enjoy a good length of tank to dart across (they are "dartfish" after all).

EDIT: Most Clowns and many Cardinals can be found captive bred. The Orchid Dotty you could find captive bred as well (although you may have to search for quite a while). The Jawfish and Firefish will be wild caught. Assessors have been raised in captivity, but I have never a CB for sale.