NCDU is a ncurses version of Linux "du" (disk usage) tool. It analyzes your hard disk and shows the amount of disk space every folder uses.
This way it's very simple to find those folders with the largest files.
You can even delete files and folders from within ncdu.
Install ncurses as described at http://www.welped.com/2007/09/03/an-easier-editor-option-for-mybook/ (<— do not work, sorry)
Read about ncdu @ http://dev.yorhel.nl/ncdu/
cd /opt wget http://dev.yorhel.nl/download/ncdu-1.3.tar.gz tar zxvf ncdu-1.3.tar.gz cd ncdu-1.3 ./configure -prefix=/usr make make install
if you are getting a compiling error. just run:
ipkg update ipkg install ncdu