Works great - very useful
Glary Utilities - The No. 1 Free, Powerful and All-in-one utility for cleaning your PC
WinDirStat - WinDirStat is a disk usage statistics viewer and cleanup tool, inspired by KDirStat.
BleachBit - When your computer is getting full, BleachBit quickly frees disk space.
TreeSize - TreeSize tells you where precious disk space has gone to.
AVG PC TuneUp - Peak performance for your PC. Keeps it going for longer. - More Speed Turbo Mode
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.