Check previous posts for a more detailed entry on these "google hacks"
The general command to search these sites is:
e.g. to look for mp3 files on rapidshare.de you would simply search in google for
You can of course enter a specific term.
list of (popular) extensions:
mp3, movie, mpg, avi, jpg, bmp, zip, rar, pdf, doclist of sites you can search