Great free software comes from all over the world from the excellent file manager Servant Salamander from the Czech Republic to this choice from Germany from the Jam Software company. 

http://www.jam-software.com/company/about_us.shtml

http://altap.cz/

You often wonder why my drive is full, you can scan it with Treeview and track down by the top 100 files, by user, by size of directory almost any way you can conceive of and clean up your hard drive space. It has great charting and visual options to see what is on your drive and how the drive space looks over time.  The paid version gets you much better analysis by different charting options and a list of features too numerous to start in on right now. Give it a try I would recommend the paid version, they update it several times a year and it has worked quite well anywhere I have needed it.

Free:

http://www.jam-software.com/treesize_free/TreeSizeFree_9x.zip

Paid:

http://www.jam-software.com/treesize/