[zx2c4]

Or, for Linux - Filelight: https://en.wikipedia.org/wiki/Filelight

[dijit]

or just ncdu on command line? :)

http://dev.yorhel.nl/ncdu

[baldfat]

WinDirStat - https://en.wikipedia.org/wiki/WinDirStat

Started out as kDirStat for KDE in Linux.

I use ncdu and Ranger file manager 95%+ of the time.