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

SequoiaView - SequoiaView is a featured rich application that comes with the visualization technique to provide you a single view of files and documents that are stored in your hard drive.

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

DiskBoss - A file manager with a focus on storage side of things: Monitoring, classing, storage, duplicate...

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.

DiskWave - DiskWave is a free utility to help you determine where most of your hard drive space is consumed.