There IS a Halo movie. It's called Halo legends and it features 7 different mini stories throughout the Halo universe. It isn't as popular or "good" as a decent movie, but it's still a movie. It isn't a blockbuster-type thing either.
Neil Blomkamp was originally going to direct the movie, but Bungie and Microsoft wanted too much money, or wouldn't properly fund or whatever, and there were problems with the script writers, so instead of waiting, Blomkamp and Jackson went ahead and directed an original movie called "District 9." I don't think a Halo movie will ever happen, sorry guys.