So far you guys all have terrible suggestions
for a 75 gallon tank!! A Powder Blue Tang, a Sailfin Tang, or a Purple Tang in a
75??? That's awful.
I would suggest a trio of Flame Wrasses or Hooded Wrasses. Why? They will never outgrow the tank. They are peaceful to other fish (besides possibly some other wrasses). They are easy to keep once acclimated and not prone to disease. They are beautiful. A trio will provide you with one super male, one sub-dominant male, and one female thus providing the best color display and likely spawning rituals as well.