Source: wall.alphacoders.com

2. Superman vs. The Amazing Spider-Man

Come on, you had to know this was coming.

As the first Marvel/DC crossover, it has very obviously earned its place on this list. And it's a really fun story.

Lex Luthor and Doctor Octopus, both recently thrown in jail by their respective heroes, decide to team up and pit them against each other. Later, when Clark Kent and Peter Parker are both covering the same news story, they are tricked into suiting up and going up against each other. Luthor blasts Spider-Man with a ray to make him super strong, allowing him to actually hurt Supes. Eventually the ray wears off and Spidey finally stops punching Superman and agrees to talk. They talk it out, and go to find their nemeses, beating them up, and throwing them in jail once more.

An incredibly fun crossover that lives up to exactly what you want to see out of it. Also, some really strong moments between Peter Parker and Lois Lane. All in all, you couldn't ask for a better first crossover.