You have a lot of choices. CLowns, basslets, dottybacks, blennies, gobies, and more. I would avoid tangs (tank too small) and damsels (too aggressive).
For a cleanup crew, I prefer inverts over fish. Maybe a dozen astraea snails, a turbo or two, and a dozen nassarius, and a few scarlet hermits to round it off. A lawnmower blenny might be good, but I worry that it would starve if there's not enough algae in a tank that size.