What!? indeed: baobab. A colleage of mine told me this was some kind of remarkable tree, but it also turns out to be a little handy utlility.
With baobab you'll get a nice overview of all the directory sizes. You can also let this utility connect to a remote filesystem. The sector view is a bit akward at first but it's quite convenient. Requires gnome. An apt-get install shows that the package is to be replaced by gnome-utils, so chances are it's already on your linux box.