Famke Janssen has signed to star as Phoenix in X-Men 3, according to Variety. X3 will be directed by Matthew Vaughn, and is currently scheduled for a late May, 2006 release.
Janssen joins returning co-star Hugh (Wolverine) Jackman, who is also slated to get his own feature film (see 'Troy Scribe to Pen Wolverine Movie'). X3 is currently being written by Zak Penn (see 'Zak Penn Writing X-Men 3').