From Linux.com :: Disk usage analysis and cleanup tools:
Baobab does for GNOME users what KDirStat does for KDE users -- search and destroy. Like KDirStat, Baobab can be used with other desktops and window managers as well. If it's not already installed on your system, find a package for your distro or download the tarball and install it.
On startup Baobab displays the total filesystem usage and capacity. You can scan all the filesystems, a selected directory, or a remote filesystem from the Actions menu. Baobab prints the directory tree as soon as it starts scanning. Alternatively, you can also enter baobab path-to-directory at the command line.