My list:

(1) Green Goblin
(2) Doctor Octopus
(3) Lizard
(4) Kingpin
(5) Kraven the Hunter
(6) Vulture(s)
(7) Mysterio
(8) Sandman
(9) Spencer Smythe & Spider-Slayers
(10) Scorpion
(11) Chameleon
(12) Electro
(13) Rhino
(14) Enforcers
(15) Beetle
(16) Morbius
(17) Silvermane
(18) Hammerhead
(19) Molten Man
(20) Shocker

What would be yours?