File-Extensions.org
The Source for File Extensions Information
File-extensions.org library contains thousands of file extensions and the database is still growing.
A large number of file type entries have detailed descriptions, including their current use and the list of programs that can open, view, edit, convert or play unknown file you search for.
ConvertCADfiles.com is now also listed here with detailed conversion capabilities: http://www.file-extensions.org/online-cad-converter-file-extensions