Writing Club Question.

So I have been a writer all my life, and I have been on the writing club here since I joined Fanpop... but I have never done this before. I am thinking about doing a fanfiction forum. As you may have seen others type up their stories on the forum and have people comment. The thing is I have written so many stories I need a fresh idea. Can you help me think of a fanfiction to do?

Fan fictions I have done before.
~Merlin (Usually consisting of Merlin/Morgana at some point)
~Percy Jackson (Once... it was "interesting" :))
~Wicked (I adore this!)
~Warriors (The cat version.)
+And many more.

Thanks you guys! I apperciate your help!