Open XML Explained - in paper or digital form
If you haven't heard, Open XML has created a lot of buzz on it way to becoming a standard.
Back at ODC, I was able to bring back a couple of copies of Open XML Explained, a book talking about the specifications (written by Wouter van Vugt). You can hit the link above to download a copy, or ping me if you want a paper copy (very limited supply).
Can you create Office documents without Office (even on the server or client)? As an example, check out Wouter's Package Explorer.