Morville and Rosenfeld's seminal IA text, Information Architecture for the World Wide Web has gone into a 3rd edition. CMSWatch has published one of the new chapters so you can go over and read it for free. It tackles enterprise IA.
If you are involved in web development and design and have never looked into this book I suggest you do so. The Library here has made the full text of the second edition available online. So now you have no excuses.