The news just broke that Josh Brolin is playing Thanos for Marvel Studios in the Guardians of the Galaxy movie.
Back in 2012, Cosmic Book News was first told that Thanos was going to be featured in both Guardians of the Galaxy and The Avengers 2.
It's possible all of this is leading to The Avenger 3, perhaps Thanos with all of the Infinity Stones (Infinity Gems and Gauntlet in the comics).
Recently, Guardians of the Galaxy director James Gunn even stated that Guardians connects to The Avengers 3.
Guardians of the Galaxy hits August 1st with The Avengers: Age Of Ultron on May 1, 2015.