ncdu - A disk usage analyzer with an ncurses interface, aimed to be run on a remote server where you...
TreeSize - TreeSize tells you where precious disk space has gone to.
WinDirStat - WinDirStat is a disk usage statistics viewer and cleanup tool, inspired by KDirStat.
Baobab - Distributor of workload automation, financial statement reporting, data access, IT Asset Management and Service Desk software solutions.
Filelight - Filelight is an application to visualize the disk usage on your computer.
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.