I think DEXplor is better for this than almost anything else.
Each directory contains a bar graph indicating what percentage of space that directory is consuming. It is relative to drive the directory is in, so it will show you the proper consumption for Main Memory, Storage Cards and even the internal Flash Disc.
The free version of DEXplor has this functionality.
The Registered Version allows you to search for files with around a dozen different attributes, including a minimum and / or maximum file size that you can specify.
The graph for Program Files shows that that directory is consuming around 20% of the Storage Memory. The Storage Card graph shows the storage card is around 33% full. The blue graphs down below are attached to files inside of a ZIP, and they indicate how well each file compressed (compression ratio). This screenshot is a bit busy, because I tried to show as many different things in a single screen as possible.
Now if you were to open up the Program Files directory you would see how much each individual directory is consuming, etc.
Dan East