Honorable Mention: Percy Jackson and the Sea of Monsters.
Admittedly, the first film, Percy Jackson and the Lightning Thief, was pretty bad. But the first book was almost infinitely better, and that holds true for its sequels. The Percy Jackson series by Rick Riordan is one of the best young-adult series I've read, and its spin-offs are likewise thrilling. If the new director (Thor Freudenthal) and new writers (Scott Alexander and Larry Karaszewski) can pull the franchise back from the brink, this could be a phenomenally successful series and a worthy successor to the Harry Potter franchise. The release date is tentatively set for late 2012.
Honorable Mention: The Adventures of Tintin: Secret of the Unicorn.
I've been looking forward to this film since I was a little boy. The Adventures of Tintin are a series of comic books drawn by the Belgian artist Georges Remi, better known as Hergé.
Tintin is not just for kids. Hergé's early works were fairly straightforward wish-fulfillment fantasy, but after a conversation with a Chinese friend, he realized the potential impact of his work, and began to invest considerable research (both historically and scientifically) into the series. For instance, his breakthrough work is The Blue Lotus, a historical fiction detective-mystery based on the Manchurian Incident of 1931 and the ensuing Sino-Japanese War.
His work, alongside that of Alan Moore (Watchmen), was crucial in legitimizing the comic book and graphic novel as legitimate forms of art and literature. Hergé was cited as a major influence by Andy Warhol, and his work is even today renowned throughout Europe.
So it was something of a big deal when Peter Jackson (The Fellowship of the Ring) and Steven Spielberg (Raiders of the Lost Ark) announced in 2007 that they would collaborate on a trilogy of films adapting the Tintin saga to the big screen. The first of these films would be based on three books: The Crab with the Golden Claws, The Secret of the Unicorn, and Red Rackham's Treasure.