Marvel Animation Universe

Marvel Animation Universe refers to a fictional universe which connects a number of animated TV shows based on Marvel Comics. Originally, there were two seperate animated universes, but they were rebooted and combined into a single universe.

Shows
Spectaular Spider-Man - The show which began the animated universe. It lasted for two seasons and was based on the animated series of the same name. At the end of season two, the show was "cancelled" but was the story was continued into Ultimate Spider-Man, which featured slightly different character designs and took a different approach to the overall plot.

Wolverine and the X-Men - Based on the series of the same name, the show introduces the X-Men and sets them up to appear later on in the universe.

Iron Man: Armored Adventures - The show on which this was originally based was not part of the first universe, but was rebooted as part of this one. It focuses on Iron Man's origin, but unlike the original show, doesn't take place during Tony Stark's teenage years.

Earth's Mightiest Heroes: The Avengers - The final part of the original universe which shows the formation of the Avengers. It "ended" with the season four finale, but like Spider-Man, carried on into Avengers Assemble.

Hulk: Agent of S.M.A.S.H. - The most recent show which focuses mainly on the Incredible Hulk.

Chronology
Iron Man: Armored Aventures

Spectacular Spider-Man

Wolverine and the X-Men

Earth's Mightiest Heroes: The Avengers

Hulk: Agent of S.M.A.S.H.