Unintended duplicate files can chew up a lot of disk space. Auslogics Duplicate File Finder will help you dupes even when the files names don't match.
By using the MD5 file hash of the files it scans Auslogics Duplicate File Finder can dig through your disks and duplicates with mismatched names. Multiple copies of music and other media, even when oddly named, will be matched up. You can filter by file size and file type. Matching can be contingent on file name, date and size, and the file hash.
If you have a favourite tool for finding duplicate files let's hear about it in the comments. Auslogics Duplicate File Finder is freeware, Windows only.