dupeGuru - dupeGuru is a tool for finding duplicate files on your computer.
WinDirStat - WinDirStat is a disk usage statistics viewer and cleanup tool, inspired by KDirStat.
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.
WizTree - WizTree quickly finds the files and folders using the most space on your hard drive. It scans the MFT (Master File Table) instead of crawling the entire disk which makes it very fast.
AllDup - AllDup is a freeware tool for searching and removing file duplicates on your Windows computer.
TreeSize - TreeSize tells you where precious disk space has gone to.