I just joined, so I'm not sure if I can or how to edit my post. I was thinking of some other cool fish you could add to your 55:
golden dwarf moray (expensive) - IMHO a snowflake or chain link will outgrow a 55
sharpnose puffer (you can't keep the leaf fish if you get one)
cherub or flameback pygmy angel - tiny, but all kinds of attitude
I used to keep seahorses in my 55. I has 3 pairs with some seahorse-safe tankmates. I know they aren't aggressive tank fish, but they are cool and not that common. I'm a moderator on seahorse.org, there is a lot of good info there.