Assuming you're not keeping triggers or puffers, then an assortment of snails and hermits would be good. The combinations are almost limitless, but here's an idea:
Astrea snails: 6
Trochus snails: 6
Cerith snails: 12
Nassarius snails: 12
Blue leg hermits: 12
Scarlet reef hermits: 6
Serpent star: 1
Emerald crab: 1
I like a large, relatively diverse, cleaning crew.