The Jim Henson Company is making a sequel to The Dark Crystal. They're co-producing it with Orphanage Animation Studios who's doing some computer animated parts of the movie, though most of the film will still be puppets. Orphanage is the baby of Genndy Tartakovsky, the guy responsible for Samurai Jack and the Star Wars: Clone Wars cartoons. He's also directing the Dark Crystal sequel.
The sequel's called Power of the Dark Crystal and it's set centuries after the first one. The plot is about a girl who's made of fire and steals a shard of the crystal in order to repower the dying sun.
I'm more of a Labyrinth guy, but The Dark Crystal was a fun movie and a sequel sounds good to me as long as they can recapture the imagination of the original. Unfortunately, that isn't a given with the Henson Company since it's founder passed away, but with Tartakovsky involved, there's much hope.