WinDirStat - WinDirStat is a disk usage statistics viewer and cleanup tool, inspired by KDirStat.
dupeGuru - dupeGuru is a tool for finding duplicate files on your computer.
TreeSize - TreeSize tells you where precious disk space has gone to.
VisiPics - VisiPics does more than just look for identical files, it goes beyond checksums to look for similar...
SpaceSniffer - SpaceSniffer is a freeWare (donations are welcome) and portable tool application that lets you understand how folders and files are structured on your disks.
Duplicate Cleaner - Duplicate Cleaner: the fastest and most popular tool for finding duplicate files. Over 1 million downloads: Get your copy now! Free and Pro versions available.