I wanna hear yours but these are mine
1.  Mr. Freeze  (Not the one with Schwartzenegger in "Batman & Robin"--The one from the Comics and the Animated Series) because he isn't crazy like most.
2.  Catwoman--a highly skilled--"Cat" Burglar
3.  Clock King--just  a normal guy who is obsessively punctual
4.  Clayface ---he is so vain--you can see his character as a caricature of our modern day society.
5. Harley Quinn---just fun and crazy