I've found internal documents written by smart people and smart companies to be infinitely better than stuff put out there for PR which tends to be weighted-down, caveated, and also more basic than the hard-hitting internal stuff.
Two of my favorites --
1. Ray Dalio's "Principles" -- from Ray Dalio, the brilliant manager of the world's largest hedge fund. His "Principles" is one of the most important and valuable reads I've found:
2. Valve's "New Employee Handbook" -- a great document on culture that provides a look at how a sharp non-traditional company does it. Quite good:
I've also found a lot of value in documents released and/or declassified by the U.S. military and intelligence services. For instance, the "Warfighting" from the U.S. Marine Corps has a lot of really clear thought and valuable lessons in it:
Got any favorites you've come across throughout the years?
A little different, but Marcus Aurelius' Meditations are a collections of his internal writings, written with no publishing intent.
It's the best book I've ever read, for so many reasons.
I like these!
Two of my favorite published internal documents are on design:
1. MailChimp's style guide for internal copywriters: http://voiceandtone.com/
2. Pixar's rules of storytelling: http://www.pixartouchbook.com/blog/2011/5/15/pixar-story-rules-one-version.html
Perhaps you could also have an "internal documents" section on your site. A compilation of experiences and business expectations. It could also link to these documents and any others you find as a go-to page for us all.