The previously un-named Marvel movie for 2014 will be Guardians of the Galaxy, according to the usually reliable Latino Review.  The film is to be announced at Comic-Con, according to the report, and will feature Thanos, who was teased in the closing of Joss Whedon’s The Avengers.  That will put four movies in the run-up to The Avengers 2, including two in 2013: Iron Man 3 and Thor 2 (see "'Game of Thrones' Helmer in Talks for 'Thor 2'"). 
Marvel Studios head Kevin Feige had previously revealed that a Guardians of the Galaxy film was in the Marvel slate, albeit unscheduled (see "'Guardians of the Galaxy' Movie").  And Disney had reserved dates for two Marvel movies in 2014 (see "Disney Reserves Slots for Marvel Mystery Movies").  It’s expected that one of those two films, scheduled for May 16th and June 27th, will be Captain America 2.  Now Guardians of the Galaxy is expected to be the second 2014 Marvel feature.  Stay tuned for the official announcements at Comic-Con.