CCleaner - CCleaner cleans, speeds up and frees up space on business endpoints.
WinDirStat - WinDirStat is a disk usage statistics viewer and cleanup tool, inspired by KDirStat.
Avast Cleanup - Next generation tuneup and cleanup for your PC
TreeSize - TreeSize tells you where precious disk space has gone to.
Advanced System Optemizer - Clean, optimize and personalize your PC
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.