The comic version of Malekith has connections with the Casket of Ancient Winters, an artifact the frost giants from the first film were very interested in.
Christopher Eccleston is known for his turn as Dr. Who in 2005. He left after a single season, claiming he didn't want to be typecast as the famous character.
Alan Taylor will be directing the film. If that name sounds familair, he's directed six episodes of HBO's Game of Thrones.
The first Thor made $181 million domestically in theaters and served as a build-up to the huge hit The Avengers. The last we saw Thor we was in The Avengers, when he was bringing Loki back to Asgard for his punishment. It's quite possible we will see hints at an Avengers sequel in The Dark World.