Checking free disk space on Debian systems

A great APT package to use for checking free disk space is "discus". Discus displays disk usage of each file system in a textual bar graph format.
Install with
apt-get install discus
Output appears as such

Mount	Total	Used	Avail	Prcnt	Graph
/	48.09 GB	3.34 GB	44.75 GB	6.9%	[*---------]
+ib/init/rw	505.4 MB	0 KB	505.4 MB	0.0%	[----------]
/sys	0 KB	0 KB	0 KB	0.0%	[----------]
+oc/bus/usb	0 KB	0 KB	0 KB	0.0%	[----------]
/dev	10.0 MB	52 KB	9.9 MB	0.5%	[----------]
/dev/shm	505.4 MB	0 KB	505.4 MB	0.0%	[----------]