5. World War Hulk
Although, in the comic books, World War Hulk required another storyline (Planet Hulk, in which Hulk was banished from Earth) to occur before it came to be, a similar scenario could be created due to the Hulk being pi**ed off by something else entirely (perhaps just being banished in to space without all the gladiatorial stuff occurring). Whatever that "something else" turned out to be, it would result in the Hulk running rampant around the world, attacking other super-powered beings as revenge for whatever had been done to wrong him. In the comic book, he attacked the X-Mansion, defeating teams of X-Men in the process, he destroyed Stark Tower, defeated Iron Man, and took on various other Avengers members, and encountered other heroes such as Mister Fantastic and Spider-Man, as well as S.H.I.E.L.D. Hulk turned Madison Square Garden in to a gladiatorial arena and forced the a group of heroes, including Doctor Strange, Iron Man and Mister Fantastic, to fight against a giant tentacle monster and then forced them to fight each other (citing it as "justice and not murder"). It resulted in a final fight in which the Sentry is persuaded to battle the Hulk, after which Bruce Banner is taken in to custody and imprisoned three miles underground. Seeing the Hulk causing havoc, resulting in a plethora of heroes stepping up to the plate to stop him, would be awesome and an ideal way to bring non-Marvel Cinematic Universe characters such as Spider-Man, the Fantastic Four and the X-Men in to that continuity.