WinDirStat - WinDirStat is a disk usage statistics viewer and cleanup tool, inspired by KDirStat.
TeraCopy - TeraCopy is a compact program designed to copy and move files at the maximum possible speed, providing the user with a lot of features.
TreeSize - TreeSize tells you where precious disk space has gone to.
Ultracopier - SuperCopier replaces Windows explorer file copy and adds many features: Transfer resuming, transfer...
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.
RoboCopy - Robocopy is a free file copy tool that is included with the Microsoft Windows operating system. It allows one to construct complicated instructions to move, or copy files.