One of the best apps in the Ubuntu Repository is Filelight.
Filelight will scan your folders or file system & show you very quickly where your hard disk space has gone. It is not easy to describe how it displays the data but check it out.
apt-get install filelight
Thats all there is to it, you will now find Filelight under
Applications –>Accesories –>Filelight
Have a look at the Filelight Website