One spot foxface for me a must have., I love the yellow wrasse lawn mower Blenny is a great asset and fun to watch. A flame hawk makes for a nice red color with grumpy eyes.
Exquisite fairy wrasse. Any species of leopard or tamarin wrasse (if you can find a healthy one), but probably the ultimate would be a regal angelfish though they are only reef safe with caution and maybe too big for a 100gallon.