This is a really neat example of how to use the advanced search abilities of Google to narrow down your search to specific files.
From the article:
The following is a Google search string for searching open web directories containing downloadable Nirvana music files. Substitute the term Nirvana in the search string for any other band of your liking. You can always bookmark the search result for future use.
With some very slight modifications the same search string can easily be used to search for ebooks in DOC and PDF format:
Or perhaps your looking for some specific video file: