Here are the characters who have had a "Top Five Most Iconic Covers" list done for them. It's in chronological order.
1. The Joker
2. Iron Man
3. Supergirl
4. Nick Fury
5. Adam Strange
6. Kitty Pryde
7. Jimmy Olsen
8. Magneto
9. Lois Lane
10. Hercules
11. Lobo
12. Hawkeye
14. Black Canary
15. Green Goblin
16. The Question
17. Red Skull
18. Punisher
19. Swamp Thing
20. The Thing
21. Hal Jordan
22. Wolverine
23. Batgirl
24. Black Panther
25. Sinestro
26. Rogue
27. Darkseid
28. Thanos
29. Barry Allen
30. Captain America
31. Daredevil