A .mp3 loop of rain falling on a roof and into a gutter. I have a .wav version, but it's 15+ mb, and my bandwitdth limit won't accommodate that. :(

Don't know how you'd use it exactly, perhaps as a background element for a rooftop level of some side-scrolling arcade game? But it loops really nicely (surprisingly, since I normally have to work for quite a while to get something to loop satisfactorily).