Clonezilla - Clonezilla is a suite of software that's designed to allow you to back-up and image new hard drives with your data.
WinDirStat - WinDirStat is a disk usage statistics viewer and cleanup tool, inspired by KDirStat.
Macrium Reflect - Macrium Software - the creators of Macrium Reflect backup, imaging and cloning software.
TreeSize - TreeSize tells you where precious disk space has gone to.
AOMEI Backupper - AOMEI Backupper is a software created to help a person backup, restore, clone, and sync their entire Windows system.
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.