Spacesniffer
[brief product description Latest release is 1.1.2.0
SpaceSniffer is a freeWare (donations are welcome) and portable tool application that lets you understand how folders and files are structured on your disks. By using a Treemap visualization layout, you have immediate perception of where big folders and files are placed on your devices. Treemap concept was invented by Prof. Ben Shneiderman, who kindly permitted the use of his concept into this tool.] From Site.
http://www.uderzo.it/main_products/space_sniffer/
Definitely a great program to find whats taking up room on your hard drive. Just download and unzip. It is self launching and requires no installation.