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.
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.
DiskBoss - A file manager with a focus on storage side of things: Monitoring, classing, storage, duplicate...
WinDirStat - WinDirStat is a disk usage statistics viewer and cleanup tool, inspired by KDirStat.
DiskWave - DiskWave is a free utility to help you determine where most of your hard drive space is consumed.
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.