Disk Usage Explorer is a easy to use program that shows a visual representation of disk space distribution on the disk.
I found that most other similar software do almost everything but leave out the most important features. The following two reasons motivated me to write this piece of software.
The ability to visually see the space distribution all the way to the leaf nodes.
The ability to selectively exclude folders/files from the graph.
Disk Usage Explorer does not allow you to modify the filesystem in any manner (i.e copy/rename/delete/move etc). However, it does allow the end-user to launch external programs from within itself which in turn can be used to make the modifications.
Disk Usage Explorer is absolutely free.