I've just installed k4dirstat. (It's almost identical to WinDirStat, if you're familiar with that Windows program. I believe Windirstat is based on kdirstat.)
The feature that I find most useful - and which is missing from a lot of disk usage software - is that you can delete files from within the program, saving the hassle of switching back and forth between nautilus or a terminal and the disk usage program to clean up files.
If you're using Ubuntu 11.10 you can't install k4dirstat from the Software Centre, but you can install a backport - see this thread: Can I install kdirstat...
glary utilities disk analysis
. And how do you decide, that a file takes too much space? A video is such as big as it is - how can a software decide: it is too big?