In addition to HTML files, Google indexes other file types like: PDFs, Microsoft Office files, Shockwave Flash files and more. Google offers you the option to read the HTML (or text) version of the cached file, in case you don't have an application that opens the file.
Google added
OpenDocument format to the list of supported documents. OpenDocument is supported by important office suites like
OpenOffice.org, Star Office, KOffice, but also by Google Docs & Spreadsheets. OpenDocument can be used to store many kinds of files, including documents (.odt), spreadsheets (.ods) and presentations (.odp).

Google's filetype: operator allows you to restrict the
search results to files that have a specific extension.
</img>
</img>
</img>