Implementing Enterprise 2.0
Highly recommended: Ross Dawson's Implementing Enterprise 2.0. I find it an excellent strategic overview of the concept, components, key issues and implementation strategies from the business/organizational/people perspective. Sample chapters are available for download on the web site. On the site as well are discusssion forums for the different chapters, and a forum for offering suggestions for "Release 2.0" of the guide.
I see this as a highly useful key resource for building common language/understanding and engaging key stakeholders on building Enterprise 2.0 strategies.