I’ve spent some of this morning packaging a PHP script I wrote a few months ago into a little Mac OS X application. It was at risk of going stale, so thought I’d let it out into the open for a bit of air. It’s called folder2dot. When you drop a folder onto it in the Finder it creates a ‘dot’ file that represents the item’s contents and sub-contents.
You can then render the ‘dot’ file with the Graphviz graph drawing tools (I recommend the Macintosh port of Graphviz) and you get a diagram of the dropped item’s contents and sub-contents. You might be able to open the ‘dot’ file using Omnigraffle (it supports a subset of the DOT language — I haven’t tried it yet!).
I found it handy to visualise the inventory of the files in a website I was redeveloping; it produces fairly plain output that is probably most useful as a starting-point.