The folks behind the trio of films based on The Chronicles of Narnia books are going back to square one as they figure out a path for a possible fourth installment. In fact, they are literally going back to square one. Rather than continue on with The Silver Chair, as many people thought they would, Walden and Fox are in talks to use the first part of the story -- and the best book if you ask me -- The Magician's Nephew as the next Narnia flick. While it was the sixth Narnia book C.S. Lewis published, chronologically in the world of Narnia, it precedes The Lion, The Witch, and The Wardrobe. It sets up the creation of Narnia, introduces the White Witch, and includes transportation to different worlds with the help of magical rings (um, hello that's awesome). I really can't see why they waited this long to adapt this particular book from the series.
As for the film series, it looks like we'll have to wait a few years before we see the next one and it's looking likely that it will get a Christmastime release. While The Voyage of the Dawn Treader didn't do as well as the other films, it did gross over $400 million worldwide, so I think it would be a pretty safe bet that they'll soon get cracking on the next one.