If you need a GUI you can check 'Diskusage'.

from http://www.gronmayer.com/it/
you can install the following repository:

anderenen.de
[Repository is online]
http://www.anderenen.de/repository
chinook | free
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Dls: 4870
several apps including diskusage, EightyOne, WifiInfo
Status: Repository is online
Project page: http://www.anderenen.de/
last update: 12/25/2007 09:57:46 (GMT +0100)
Package:
diskusage (v. 0.1.20071223-1)