Surprise! You don't need to come up with original ideas for writing all the time! Fan fiction "lets" writers add to or continue existing stories/books. Best part: "beta readers" will read your drafts and give you feedback before publishing to the rest of the world! This is a VERY supportive community.
Wow - online editions of books! (And some Mad Libs.) Some might be a little too easy for middle school students, but let's face it: we're never too old for Mad Libs!