I had a Kole Tang in my 55g reef that worked out great, and it was constantly picking at any algae that grew. I love the dwarf angels, but they're too risky to get for a reef, you never know when they'll develop a taste for coral. Be careful with getting anything that is very small or passive, the six-line will be likely to terrorize it until it dies. So whatever you decide on, make sure its bigger than the wrasse.
In addition to the Kole tang, you may also like the chromis, cardinals, damsels, maybe one of the smaller anthias, blennies are pretty fun to watch, and a diamond watchman is always a good addition that keeps the sand clean and doesn't take up any swimming space.