http://www.nirsoft.net/utils/search_my_files.html
Duplicate Search Mode
Starting from version 1.35, SearchMyFiles also allows you to search duplicate files on your system. In order to use this feature, simply change the search mode in the 'Search Options' window to 'Duplicates Search'.When you switch to 'Duplicates Search' mode, all other search options are still relevant, and SearchMyFiles will scan your files according to these settings. For example: if you choose to search for files larger than 500KB, SearchMyFiles will only search for duplicate files that their size is larger than 500KB. In fact, it's highly recommended to narrow your duplicate search by using date/size restrictions, because if you don't do it, the duplicate search will be very slow, and it'll consume a large amount of memory.
When you are in 'Duplicates Search' mode, SearchMyFiles will first scan all files and folders according to your settings, and only after the scan is finished, it'll locate the duplicate files and add them to the files list on the main window. SearchMyFiles automatically mark the duplicate files with identical colors (up to 64 different colors). There is also a 'Duplicate Number' column, which displays identical number for each chunk of duplicate files. You can click the 'Duplicate Number' column header in order to sort by this column and to easily view the chunks of duplicate files.
Be aware that the duplicate search is done by making a binary comparison of the files with the same size, byte by byte.
