Heat Vision and Deadline report that Alice Eve, last seen as the hottie in She's Out of My League, has joined the cast of 20th Century Fox's X-Men: First Class, which is being directed by Matthew Vaughn. Eve will play Emma Frost, the "White Queen" who eventually became a member of the X-Men and was seen briefly in some of the earlier X-Men movies (in Wolverine as played by Tahyna Tozzi).
Marvel has also confirmed that Michael Fassbender will play Magneto in X-Men: First Class and also that Tommy Lee Jones will play Colonel Phillips in Captain America: The First Avenger, as previously reported
So far we know that the former Bryan Singer "relaunch" of the X-Men franchise includes James McAvoy as Professor X and Michael Fassbender as Magneto as well as Eve as Emma Frost. There have been rumors that Aaron Johnson or another young actor might play Cyclops, but officially Marvel/Fox haven't announced any other cast members/characters. I'm not sure if Heat Vision's hints that Frost "has telepathic powers and as the White Queen wore scantily clad costumes" means that's the version of Emma Frost we'll see in this, but Eve is a hottie and I'm sure they'll playing up her sex appeal in this.
We'll keep you updated on all the latest!