I dream a lot (daydreams AND nightly dreams) and often get inspiration from those fantasies.
I always lose my footing when I start writing for my readers instead of just for me, the spark simply leaves me when I worry too much about how my story will be received- so most important for me is: if I sit down, I always tell myself that I won't publish this one, that I just write it for myself... that always works best.
Also very inspiring: pictures. Whenever I don't know what to write, I experiment with Gimp, do some filthy collages or simply look at screencaps.