SizeReporter is a tool I wrote that comes with no GUI. The main trigger for creating this tool was to have a way to run a disk space reporting application under a service and get raw data only. Further processing and own reporting/diagramming can then be done in a custom way by using other Software. I was amazed that for Windows I could not find anything free that actually fit my needs.
The tool is not actually really spectacular but can deal with many quirks and issues on filesystems (bad timestamps, very long paths, junctions, ...). "du" (sysinternals) was the tool I used in the past but delivers only a summary.
I hope this can also be useful to others.
SizeReporter download page