That Tall Man thing mentioned by Colten isn't a Slenderman movie, I forget what it's about exactly - but it's not Slenderman.
In my opinion, I think Slenderman stuff is best done by indie filmers and as a sort of "follow my real-time story" thing - not a movie. Like Marble Hornets or EveryManHybrid. It just doesn't seem like it's going to be done right. I want to hear what Dr. Block has to say about this, I know he's an avid Marble Hornets/Slenderman fan.