HD Tune - HD Tune Pro is a hard disk / SSD utility with many functions. It can be used to measure the drive's performance, scan for errors, check the health status (S. M. A. R.
WinDirStat - WinDirStat is a disk usage statistics viewer and cleanup tool, inspired by KDirStat.
FakeFlashTest - Tests USB Flash drives and Flash memory SD cards to determine if they are fake (not full capacity).
TreeSize - TreeSize tells you where precious disk space has gone to.
USB Memory Stick Tester - Test for USB memory sticks
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.