The Hobbit: The Official Movie Blog looks like it has some promise. Created shortly after announcements of movie plans were made public this site showed up on the www.
Of course it is very small now but in time and care this site may grow as the movie goes into production. Right now it has a small but active community with a message board, fan photos page and video page with the promise of more.
No doubt New Line Cinemas will create their own official site. But for now there is a place to visit which has it's priorities solely on news regarding The Hobbit, the movie.