A lot of fans have been speculating that one day the Avengers will team up with Guardians of the Galaxy to take on the villain Thanos. That's one of my big theories. Marvel Studios President Kevin Feige addressed this scenario in an interview with IGN saying:

"I don’t know. Part of the fun of the comics is that could happen. Any character could interact with any other character because they inhabit the same time period and the same universe. And certainly it is the inclusion of Thanos most specifically that is a declaration to audiences who are paying attention that this is connected to those other universes. Part of the fun is that it could happen someday. I don’t know when that would be. Or maybe I know and I’m not going to tell you!"

The guy isn't just going to give up their Marvel cinematic universe plans, but I'm pretty confident that a joint adventure with these two superhero teams is going to happen. I just don't know when.