Definitely Zira and Scar. Both are very well-developed. Others include:
Cruella DeVil (101 Dalmatians) - gotta love a stylish, eccentric villain
Frollo (The Hunchback of Notre Dame)
Hades (Hercules)
Mother Gothel (Tangled)
Jafar (Aladdin)
Pete (Mickey, Donald and Goofy: The Three Musketeers)
Edgar the Butler (The Aristocats)
Radcliffe (Pocahontas)
Ursula and Morgana (The Little Mermaid I & 2)
Clayton (Tarzan)
Professor Rattigan (The Great Mouse Detective)