Everyone has recommended some very nice fish, and chromis or Talbot's damsel would be my choice.(Talbots by the way, are nice, non-agressive too) and firefish or anthias. Yes, most likely, in a school of anthias, nature would probably take over and make 1 a male, but...
However, from all I've read over the years, schooling is a "threat management" response, and after it's discovered that there is no danger, they tend to become free swimming. Although they might still group up from time to time. Also, even with chromises, I think the pecking order will apply, and the weakest one tends to get killed off...