There are also a lot of cool fairy wrasses, pseudochromis, and gobies that would work well. There are also several species of dwarf puffers that would go great.
If you can find it, a speckled sandperch is awesome! They don't seem aggressive, but don't let them fool you! This guy has a smaller mouth, but he uses it! He's also got a ton of personality and will burrow tunnels under your live rock . . . He won't bother your other aggressives, and they would be wise not to bother him I often find him just "perching" on a rock and watching me in the room. Excellent tankmate. (But very difficult to find).