It seems old tip but I found this only recently. To search files like mp3 or other smaller files from Google - e.g. if you want to find mp3 for a certain song, say, "hips don't lie", do
intitle:index.of + "mp3" + "hips don't lie"
To get results having no *.htm or *.html files, you can do
intitle:index.of + "mp3" + "hips don't lie" -htm -html
The results give a lot of locations to download the files from, sites that are normally hard to find.
