Ideas just come to me most of the time. I'll be sitting at my desk either at work or at home and BAM! I get hit between the eyes with something. Eight times out of ten it's pure unadulterated shit and not worth my time, but the other two times - well let's just say I can bang out one hell of a story.
In all seriousness though - I get my ideas from day to day crap. I once wrote a story about what a leaf thinks as it's sailing down to the ground after falling off of the tree. Granted I was in fifth grade at the time... I wonder if I still have it somewhere?
Songs, documentaries, TV shows, books, my kids, my family, my friends... they all give me something. I was sitting around with a bunch of friends at work one day and we started talking about what scares us most. I brought up the fact that clowns can make me shake in my boots - BINGO! Instant fanfic!