Frameworks and libraries with it's links to documentation.
Project layers and each layer's responsibility.
Version!! If we tagged the version in the source control, then I don't see a reason to include the changeset/revision.
List of features added from the previous version.
List of known issues. (unresolved bugs).
Roadmap This is actually one of my favourite documents. I find this document very important in helping us know where we are standing, and what the customers expectations of functionality in the short and long term are. Maybe this document is more of a "Project management" document than a development-related document, however, it is always good to keep customer's priorities in mind. Another thing that I get from this document is how well we know the customer needs. If we can't manage to get a decent Roadmap, then we are failing to understand the customer's need, and that's not cool. On the other hand, if we do manage to get a decent roadmap, but this roadmap changes too often, then the customer is failing at setting their own goals.