WinDirStat - WinDirStat is a disk usage statistics viewer and cleanup tool, inspired by KDirStat.
Total Commander - A Shareware file manager for Windows® 95/98/ME/NT/2000/XP/Vista/7, and Windows® 3.1.
TreeSize - TreeSize tells you where precious disk space has gone to.
Double Commander - Double Commander is a cross-platform open source file manager with two panels side by side.
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.
XYplorer - File Manager for Windows