If you want a neat way to visualize what programs and files are taking up space on your device (whether it’s on main memory or on internal storage/storage card), take a look at MobileMonger, a free program from James Boman. It requires .NET Framework 3.5 and will only work on touchscreen WinMo devices.

As an example of how you’d use this, you can tap and zoom in on My Documents (or any directory), and move/eliminate pictures or documents that are unnecessarily taking up large amounts of space based on what you see on the screen.