My picks:
1) The Burglar
-He killed Uncle ben. Number one villian ever. Also, he nearly killed Peter and Aunt May when he returned years later, looking for the same money he was after the first time around. His final showdown with Peter is probably the most memorable send off to any villian...second only to the death of the Green Goblin in ASM#122, which was undone later on. I can't believe I'm the only one who listed him as my first choice...
2) Green Goblin/Norman Osborn
-No one pushed/pushes Spidey's buttons like this guy does. He's always there waiting for a time to strike.
3) Doc Ock
-Simply unpredictable. Every time Spidey fights him, he never knows what to expect. The only reason he's number 2 is that he doesn't make it as personal.
4) Hobgoblin/ Roderick Kingsley
-THE most cunning foe Spidey has ever faced, simply because he managed to avoid capture...or even the discovery of his true identity for so long. He kept his sanity, and used that advantage to manipulate the criminal underworld and keep Spidey guessing.
5) Kingpin
-Criminal mastermind who remains pretty much untouchable to this day. No matter what happens to him, he always seems to come up smelling like a rose. Also, he keeps all the criminals in business in New York...that has to keep you in the top five.
6) Jackal (PRE-resurrection/90's clone saga)
-This man was so obsessed with Spider-Man that he cloned his dead girlfriend, and then cloned the man himself...and he even made Spidey question his own authenticity! He gets into the top 5 simply for the torture factor of cloning Spidey's lost love.
7) Kraven
-Once a joke, now a legend. Any man who goes to the great lengths Kraven did to lash out at Spidey, as well as prove his own worth, is definitely a force with which to be reckoned. He defeated Spidey without question, and even took his place.
8) Green Goblin/ Harry Osborn
-Peter's best friend and worst enemy. His was the most tragic tale, simply because Peter couldn't save him. He earns points simply because Peter, whether he could have actually beaten him or not, couldn't bring himself to take down his best friend.
9) Scorpion
-Not Gargan/Venom, but THE SCORPION. He was a determined foe...with superior strength and speed to Spider-Man. It's a shame that he was never fully utilized, and Venom pretty much tok over his role, as he became somewhat of a joke.
10) The Lizard/ Curt Conners
-A very Jeckyl/Hyde type of foe. One one hand, he's a friend to Spider-man, and an occasional confidant as Curt Conners, and, on the other hand, he's a deadly predator who is bent on the destruction of mammals, as the Lizard. Gotta love that.