SpaceMonger - SpaceMonger helps you understand what's occupying your hard drive and more effectively clean it up without worrying about losing anything important in the process.
ZetaWatch - Manage ZFS volumes in the menu bar
Baobab - Distributor of workload automation, financial statement reporting, data access, IT Asset Management and Service Desk software solutions.
WinDirStat - WinDirStat is a disk usage statistics viewer and cleanup tool, inspired by KDirStat.
Filelight - Filelight is an application to visualize the disk usage on your computer.
DaisyDisk - DaisyDisk is a disk analyzer tool for OS X that visualizes hard disk usage and allows to free up hard disk space.