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.

Disk Usage Reports - Disk Usage Reports is a web-based way to view disk usage on remote computers or servers, or to...

WinDirStat - WinDirStat is a disk usage statistics viewer and cleanup tool, inspired by KDirStat.

TreeSize - TreeSize tells you where precious disk space has gone to.

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.

JDiskReport - JDiskReport enables you to understand how much space the files and directories consume on your disk...