NarniaWeb is claiming an insider report that Prince Caspian, the second book of the Narnia series, will begin filming soon and is set for a December 2007 release.
Reportedly, Disney was hoping for a $60,000,000 opening weekend and the film grossed over $65,000,000.
My bet is that they begin arranging filming so that one picture is released every year, perhaps even more frequently. The books are not like the Harry Potter series, where Harry is pictured in virtually every scene. Several of the books have little or no involvement with the Pevensie children and the studio could theoretically film 3 or so movies simultaneously.