This is a pretty simple question. Assuming you know what WinDirStat &/or Disc Inventory X do, which is visualize the usage of your hard drive on a file-by-file basis, sized in proportion to the size of the given file(s) & colorized according to type.
For someone it might be a new app idea. I'm hoping it already exists, however. I know a program like this wouldn't (need to) tell you the "path" to any files, but it would be nice to visualize which apps are hogging the most of the 16GB hard drive on my iPhone.
I'm aware of iTunes's simple Apps/Music/Video/Etc pie chart but am looking for something a bit more "WinDirStat/Disk Inventory X"-like.