Hey,
I also like the 6-Line Wrasse. Cool fish! Other candidates would be a pair of Firefish or a Lawnmower Blennie. The Lawnmower isn't very colorful but is neat to watch. Or, a longnose hawkfish, or.....
It all depends on what you like, just make sure you do the research first, then get the fish. (For instance, you don't want another Tang since the one you have will get cramped in a 58 gal tank.)
Good luck, and enjoy!