Anastasia Steele
At the beginning of the series, Ana is an English Lit major who is very shy and kind-hearted, and is physically described as fairly plain and pale but pretty and slim. Obviously she has to become slightly more assertive when she gets together with Mr Grey, but Ana basically needs to be someone intelligent and nice to look at but not anyone too outrageous in body or mind.
Emma Watson
Many women who grew up with the Harry Potter series already want to be her and, to be a little crude, Im sure many men wouldnt exactly mind seeing her sexy and grown up after the many inevitable schoolgirl fantasies. Having already moved on from being Hermione Granger with a bad girl role in The Bling Ring in particular, her shots in the recent trailer are shocking teenage fans and excitable men alike. She has the right subtle and somewhat bashful look, is unquestionably pretty and is known for being intelligent, not sexy.
Kristen Stewart
With the Twilight saga now over, Kristen needs a new franchise for people to extreme love or hate and rant or rave about. She has the right mousey look and there are even comparisons in that Ana and Bella Swan both seem too whiney and unsure when around the man they supposedly love. Kristen can also be assured that she will still have at least one other character professing interest in her, maintaining those love triangles we cant escape.
Jennifer Lawrence
Now a popular and almost ever-present Oscar contender (The Hunger Games and X-Men were already fighting over her, now there will be even more), Jennifer is coy but sexy, naturally curvy and has long luscious locks, so she would look like the normal girl Ana is supposed to be whilst still reaching attractiveness quotas no doubt set in place for the role. The only problem with Jen is that, as pointed out by Seth MacFarlanes We Saw Your Boobs song at the Oscars this year, she has so far managed to avoid nudity, and it seems like she wants to keep this track record for now. However they handle the graphicness and nudity in Fifty Shades of Grey, it is extremely unlikely that shed be able to get away without showing anything.