I have a brand-new, unbranded replacement N900 in my closet that I only booted once to confirm it's working. It has never seen any network connection or other interaction with the outside world since it left the factory (assuming that the seal on the box was genuine).
So I could provide a list of all installed files including the md5sums. But I'm clearly too lazy to search for and put up an explanation for every file on the resulting list. Therefore I'd propose to put the list into a wiki article so that everybody can contribute to it.

One thing that would have to be considered is that this N900 is the German variant, so it will most likely have some extra localization files and I wouldn't even want to exclude that some of the proprietary applications actually differ between different countries, be it due to a poor non-modularized implementation or country-specific laws.