Tomini tang, starry blenny, tailspot blenny, red-lined wrasse and leopard wrasse to name a few.Definitely don't have the room for any Tangs or Foxfaces in the 50.3! hah
I'm not too familiar with Blennies - I know of the Lawnmower Blenny but I don't know if I'd have enough algae to keep them well fed.
I believe most of the beneficial parasite eating Wrasses are too big for my tank as well, minus the Six Line.