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.
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.
DiskBoss - A file manager with a focus on storage side of things: Monitoring, classing, storage, duplicate...
TreeSize - TreeSize tells you where precious disk space has gone to.
DiskWave - DiskWave is a free utility to help you determine where most of your hard drive space is consumed.