Dup Scout is a handy tool for electronic discovery professionals. It allows you to search for duplicate files on local and network drives. A trial version can be downloaded here.
Click on 'Duplicates' on the upper toolbar. You'll be given the chance to change the default options and choose to search for any one of five hash values.
Select a specific directory, and Dup Scout will search for duplicate files, provide a summary of the size taken up by each subdirectory and generate a list of how many files are present in each format.
Click on 'Charts' on the toolbar, and Dup Scout will display a pie chart showing the number of duplicates for each file extension.
Happy E-Discovery Day!