Word on the street is that one of the reasons why Pixar has had a change of heart is because their executives have been given unprecedented access to "Circle 7;" a secret Disney division formed under Michael Eisner. This super top secret division is said to be specifically in charge of producing Pixar sequels of mass destruction. Now, if that's not supposed to freak you out, I don't know what is.
Currently, production has already started on Toy Story 3, and there will soon be an announcement regarding another sequel which will be chosen amongst several scripts. So far it seems the frontrunners include Finding Nemo and Monsters Inc.