SysGauge - SysGuage is a responsive software utility that monitors the memory status, CPU usage, as well as network and disk activities of your system.
WinDirStat - WinDirStat is a disk usage statistics viewer and cleanup tool, inspired by KDirStat.
Big Meter Pro - Big Meter Pro is a utility that monitors the disk and memory of your CPU.
WizTree - WizTree quickly finds the files and folders using the most space on your hard drive. It scans the MFT (Master File Table) instead of crawling the entire disk which makes it very fast.
Process Lasso - Process Lasso is NOT yet another task manager.
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.