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.
Scanner - This tool uses a sunburst chart to display the usage of your hard disk or other media.
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.
IntoDisk - IntoDisk is a tool that helps to analyse your disk space and explore it easily.