I can't really find a great disk analyzing software for Ubuntu.
The default apps in Ubuntu, Baobab (and df -h) do work, but there are no advanced features.
What I am looking for is like glary utilities disk analysis, to search for those file that take too much disk space.
Two easy options, both available in the Software Center:
GDMAP
Filelight
If neither of these meet your needs,edit your question with the specific features you want. That helps us understand your question better.
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...