I've become quite addicted to FanFictions recently.
For those out there who don't know what a FanFiction is, it's essentially what the name suggests: a fiction about a certain movie/novel/comic/game written by fans. As you can gather from this short description, the characters used normally are not invented by the writers themselves (though quite a lot of them put in original characters as well), but come from the movie/novel/comic/game in question.
Even before I knew what a FanFiction is - or ever thought of writing them myself -, I liked thinking up my own ways of how a story could have ended, especially with long-running series where you have a lot of time to speculate about the end until you finally see or read it.
When I read an article in a magazine ("MangasZene", a magazine about Manga and Animée I read regularly) about FanFiction which also included some links, I tried them out and got interested.
Currently I'm following some "Harry Potter"-FanFictions (namely the second edition of "The Deception of the Vindictive" running under the title "The Rise and Fall of the House Black" and the sequel to "Mirror Image" titled "Blurred Reflections") and I am browsing regularly through the sections for Animée/Manga (for "Gorgeous Carat", "GodChild" and "Yami no Matsuei"), TV ("Smallville" - I know I need help) and Novels (usually only "Harry Potter", but I've also browsed through the "Sherlock Holmes"-section).
Even though it first seems a bit pointless - writing stories about stories, essentially -, it's quite interesting, because the writer's ideas usually go in a completely different direction. The stories portrait people in a different way (sometimes very different, that's what is called OOC [out of character]) and show different points of view. In addition some of the writers are pretty good.