small fish:
royal gramma, orchid dottyback, other similar basslets or dottybacks/pseudochromis.
wrasses - sixline, hoeven's, fairy wrasses
firefish, blennies, gobies, cardinals, the list is endless.
then there are the usual damsels and chromis, but i dont like em much.
i think a trio or more of regal or yellow tang would look killer in that tank.