FileInfo.com - FileInfo is the central file extensions registry and contains a database of over 10,000 file types.
File-Extensions.org - Large computer file extension library with detailed explanation of each file type with links to download free or associated software programs.
FILExt - Open, view and convert files online
FileProInfo - It's All About Files, Software, Online Tools - 100% Free
Convertio - File Conversion in the Cloud
OpenWith Enhanced - OpenWith Enhanced description and features