There are a plethora of great books on software development out there.  Here are a few of our favorites.

Becoming Agile - Not to be self promoting, but we are proud of our book and we think it is a great guide for migrating to agile, and also for demonstrating what an agile process looks like in practice.

Agile Estimating and Planning - Mike Cohn is the expert on this subject.

Agile Project Management - Jim Highsmith wrote this superb book.  Greg Smith was introduced to agile by Jim.

Agile Testing:  A Practical Guide for Testers and Agile Team - Lisa Crispin and Janet Greogry