Although freeware SequoiaView has been around for a while it is nonetheless a good application.
"SequoiaView uses a visualization technique called cushion treemaps to provide you with a single picture of the entire contents of your hard drive. You can use it to locate those large files that you haven't accessed in one year, or to quickly locate the largest picture files on your drive".
Besides, there have been many new members here at CDFreaks since it's release that have not been made aware of it's existance.
Although I alluded to SequoiaView in another thread I believe it deserves it's own thread. http://www.win.tue.nl/sequoiaview/
One other thing, although SequoiaView was developed at the Technichal University Eindhoven which is located in the Netherlands, the original concept of treemaps was started at University of Maryland (See this link for History). Open-source is a wonderful thing.
P.S. Although, there are other app's. that in principle do the same thing as SequioiaView those are usually payware.