Over the last 5 years, DotNetNuke has been blessed a large number of books being written about the platform.  I was fortunate to be part of the team that co-authored a couple of the first books on the platform, and I continue to try reading every book that comes out on the platform.  Some books, like Professional DotNetNuke 5: Open Source Web Application Framework for ASP.NET cover multiple aspects of the DotNetNuke platform and is a great book for Administrators, Developers and Designers, but it necessarily can’t cover every topic in depth.  Other books, like DotNetNuke Module Programming, are narrowly targeted at Module developers.