this command was an awesome fine for me
Code:
du -k /foldername | sort -n | tail -10
finds the 10 largest folder and sorts it by size. it looks like you already have the largest offenders though:
cpanel, log, lib, and spool.
so you could start with log and see if your logs are rotating properly or just rotating out until the drive fills up. spool, do you store mail on this server, I mean do you pop or mostly webmail (so it stays on the server)
cpanel (no idea)
lib, looks like you have lots of goodies installed. maybe my command above substituting /var/lib for the foldername will tell you the biggest offenders