Spider-Man's most infamous and dangerous enemies are generally considered to be the Green Goblin, Doctor Octopus and Venom.  Like Spider-Man, the majority of these villains' powers originate with scientific accidents or the misuse of scientific technology, and they tend to have animal-themed costumes or powers.  Spider-Man, somewhat of a lone wolf, has on occasion teamed up with other spandex-clad heroes, such as Daredevil, the Black Cat, and the Avengers to battle the forces of evil in the Marvel Universe.

One of my colleagues recently brought to work what I consider to be the greatest Spider-Man team-up of all time.  In 1976, Marvel Comics and Planned Parenthood collaborated on a Spider-Man special on teen pregnancy. The villain, Prodigy, is an alien who wants teenagers to crank out babies so he can steal them and take them back to his home planet (Intellectia, of course!) for slave labor. To further his plans, the villain launches a campaign of misinformation to lull teenagers into having wanton unprotected sex.  Devious!!!

Of course, in the end Spider-Man hitches a ride on a helicopter, cracks the skulls of the Prodigy's goons, and exposes the Prodigy and his nefarious plan.  The day is saved and Spider-Man and Planned Parenthood teach everyone a good lesson about not taking sex advice from interstellar villains with dreams of galactic dominance.

The above plot summary just can't do this thing justice, so I found the entire issue on Andrew Farago's LiveJournal page. And if you really need to get your own copy, there may still be a few available on EBay.  Happy ready, True Believers!