Does Starcraft 2 contain a cooperative multiplayer campaign mode?

Solution 1:

The story driven single player campaign can only be played by one person and cannot be played by more than one player.

However, there is one mission that has been altered that allows 2 players to try this mission on different difficulty settings. http://us.battle.net/sc2/en/game/maps-and-mods/mods/left-2-die

As far as community created multiplayer maps, there are numerous survival types of maps out on the custom games list that players play versus an AI, some are story driven, some are survival. Select join a custom game, then in the category drop down select "Co-op vs. AI"

Edit

As of the latest expansion there are coop missions that can be completed with friends. The missions range in difficulty and characters that you can choose. They are designed to be completed with a friend. It is called "Allied Commander" mode. There is a much longer blog post from the Blizzard website, and you can check out the preview video here.

Solution 2:

This question is old, but in the arcade, you can maps for all 3 of the of the base games. The maps were made by RaegLordDZ and allow for not only 2 player, but also 3 player campaigns, as well as adding a ton of new content. (for example, in HotS there are now 3 strains for each evolution, and players can individually pick which one they want)

to find them either search for Raeglorddz or "Coop" in the arcade section.