There are plenty of graphical tools to do this (e.g. Baobab, KFileLight), but they are typically slow and/or inconvenient (consider a GUI-less server). I often find myself running du on the command line (over ssh) and wishing for something more visual.
Enter du2webtreemap!
ssh someserver du /path/to/somewhere > du.txt
du2webtreemap --html < du.txt > du.html
xdg-open ./du.html
Or run ./demo.sh to see something quick and local.
These days I mostly webtreemap-du this via https://github.com/ProgrammersOfVilnius/pov-server-page rather than directly.
This is based on webtreemap (https://github.com/martine/webtreemap), which was conveniently imported as a git subtree via
git subtree add --prefix=webtreemap https://github.com/martine/webtreemap v1
Note: webtreemap master is a full rewrite with a different API and a divergent commit history. Updating to use it will be fun!