In another of those secrets that wasn't really a secret Marvel confirmed the news that most everyone knew already. Vin Diesel of Fast and Furious fame has been tapped to be the voice of Groot for the upcoming Guardians of the Galaxy movie. The movie will be out August 1st 2014.
Source: Marvel.Com
http://marvel.com/news/movies_tv/2013/12/21/21680/official_vin_diesel_to_voice_groot_in_marvels_guardians_of_the_galaxy
