Auslogics Duplicate File Finder

Auslogics' Duplicate File Finder is a great free utility to help determine where duplicate files appear on hard drives or network directories. It can be downloaded here:

It can be set to find duplicate files which have been named differently, and to locate files with identical or differing file dates.

Its default settings will ignore files saved to folders usually containing system files and it uses file masks to ignore common system file names (e.g., any files with the extension .dll; .ico; etc.)