Books I Recommend:

Extreme Mindstorms by Dave Baum, Mike Gasperi, Ralph Hempel, Luis Villa

Buy it at Amazon.com

I'm biased towards this book because I wrote some of it, but I still think it's the best book out there for advanced Mindstorms users.

If you feel that the RCX-Code environment hems you in and you want to explore alternative software like NQC, pbForth, or legOS, then this book is for you.

If you want to learn more about how the sensors work and perhaps try your hand at making sensors, the section by Mike Gasperi is a goldmine of information

Creative Projects with LEGO Mindstorms by Ben Erwin

Buy it at Amazon.com

Ben has put together a delightful book that will help parents and teachers to work together with children to build interesting robots with Mindstorms.

The effort that Ben has put into making the projects accessible to children shows. With full color illustrations on almost every page, stories from children, and kid-friendly projects, this is one resource you can't do without.