Baobab
Open Source
Baobab is a disk usage analyzer is a graphical disk usage analyzer for GNOME.
ncdu
Open Source
ncdu (NCurses Disk Usage) is a disk utility for Unix systems.
Filelight
Open Source
Filelight is a KDE graphical disk usage analyzer, part of the KDE Utils package.
JDiskReport
Free
JDiskReport enables you to understand how much space the files and directories consume on your disk drives, and it helps you find obsolete files and folders.
GD Map
Open Source
GdMap is a tool which allows visualizing disk space.
Compare SpaceMonger with alternatives
Compare JDiskReport and SpaceMonger and decide which is most suitable for you.
Compare Filelight and SpaceMonger and decide which is most suitable for you.