thenammagazine
Super Freak
Read the interview, and like I said above. Reasons for why the Joker isn't going to be mentioned isn't the same as planning a third movie that was going to include him. There is no fact that supports that idea.
Been discussed before. Void would know better than I, but there was an interview where he stated they'd be exploring more of the Joker in the sequel to TDK since TDK's story was about Dent.