Server :: Root File System At 100 Percent Capacity - Why

When I try to install anything recently, I was getting errors about "No Space". I noticed that the root drive (/dev/sda1) has 100% usage which I'm not sure how that suddenly happened.

Code:
tom@HouseMedia:/$ df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda1 9.0G 9.0G 0 100% /
none 1.5G 552K 1.5G 1% /dev
none 1.5G 0 1.5G 0% /dev/shm
none 1.5G 300K 1.5G 1% /var/run
none 1.5G 0 1.5G 0% /var/lock
none 1.5G 0 1.5G 0% /lib/init/rw
/dev/sdb1 294G 182G 97G 66% /mediastorage

There was a powerloss recently and I wondered if some serious corruption had occurred. Since I'm checking the root drive, I had fsck run after a restart:

Code:
sudo shutdown -F -r now

FSCK went to work, briefly, and the logs (/var/logs/checkfs and /var/logs/checkroot) remain empty. Speaking of log files, I had a look at all of them and they take up a mere 32MB, so that's not the issue...

Code:
tom@HouseMedia:/var/log$ ls -h -l
total 32M
drwxr-x--- 2 root adm 4.0K 2011-06-05 06:39 apache2
drwxr-xr-x 2 root root 4.0K 2011-01-20 10:43 apparmor
drwxr-xr-x 2 root root 4.0K 2011-06-01 06:37 apt
-rw-r--r-- 1 root root 0 2011-03-01 06:43 aptitude
-rw-r--r-- 1 root root 851 2011-02-08 10:08 aptitude.1.gz
-rw-r----- 1 syslog adm................

Using Code:
du -h
I know that:
/var uses 1.2 GB
/root uses 100 K
/usr uses 1.4 GB
/tmp is empty
/home has 35 MB

Have already ran apt-get clean. How can I figure out what is taking up so much room? How can I go about figuring out what is huge and is safe to remove?