Here ya go:
http://www.throttlelauncher.com/port...age/tstorage01
Description from site:
Have you ever though.... where is my storage space going to!!.... This is a new app I've developed!! Smile. It shows you graphically how your storage space is beeing used displaying a circular chart so you can eassily locate which folders are taking more storage. You can navigate through all of your folders and analize each one in detail or exclude them from the report. Eassy and simple!!
Another option:
MobileMonger is a tool to show storage space use on your Windows Mobile in a TreeMap.
Main Memory fills up pretty fast on the Diamond if your not careful to install absolutely everything to the storage card, and also set your default save location to the storage card.
When running out of Main Memory I wondered what was using it. If you hit the link provided in the Windows Mobile memory settings screen it takes you to an explorer window that shows you all files greater than 64kb