Here's a listing of some of the more outlandish people that have been fingered as being involved, mentioned as likely candidates, or are interested in the movie in some form or fashion.
Selena Gomez. While it'd be a little awesome to see the white-washing of various book characters go in the opposite direction with the casting of a Hispanic actress, I just don't see her as being really right for the role. Maybe it's because she's too young. Maybe it's because she's too dominant. Either way, the rumor of her being Ana just seems really silly, but since Gomez has already shot down rumors of her being in the film I suppose we don't have to worry about this overly much.
Shia Lebouf. No. Just no. While Lebouf does seem to have the douchebag aspect of Christian Grey down, I can't see him being dominant enough to play Grey. Every time I imagine him trying to top someone, I just picture the other person getting irritated and turning him into a Shia sized floor mop.
Miley Cyrus. OK, so she's been listed on a website as being a likely candidate for the role of Anastasia Steele. I'm now picturing her as Ana to Shia's Christian. It's not a pleasant image and I'm currently wondering if I can self-lobotomize if I shove a pencil far enough up my nose. I know that Cyrus hasn't really acted up that much lately, but I just imagine her wandering around Grey's apartment stoned out of her gourd while Lebouf just sits in a corner and practices being the world's largest wet rag. Imagining them in the infamous tampon sex scene is a little warped because I keep seeing the roles switch around and having Cyrus remove Lebouf's tampon because she's just that much more masculine and dominant than he is.
Justin Bieber. That's right folks, Justin Bieber. Depending on where you go, he's either up for an undisclosed role or he's been asked to play the role of Christian Grey himself. All jokes of him being more likely to play Ana aside, I'm finding it highly unlikely that the Biebs would be capable of playing a guy that's in his late 20s, unless he's supposed to be playing a teenaged Grey and that character doesn't entirely appear until book three. And yes, I think Bieber could kick Lebouf's butt.
Charlie Sheen. Somewhere, someone has said that he was in the running to play Grey, to which Sheen actually said that he wasn't interested. Sort of. I'm actually a little sad that this one is so obviously false, because it'd be kind of awesome if he was. The producers could put him and Cyrus together in the film and let them "do as they will", resulting in a drunken drug filled bacchanalia that would go down in history. They're already friends, so you wouldn't have to worry about them fighting on set. On a side note, I can see him being dominant enough to play Grey and if the movie was going to be a parody of the book, Sheen would be their best bet by far.