Stuff on lean manufacturing (yes. manufacturing!)
Agile Software Development with Scrum by Ken Schwaber and Mike Beedle.
I used this book as the starting point to understanding Agile development.
These two are great resources on SPM and methods therein:
Software Project Survival Guide - Steve McConnell
Rapid Development - Steve McConnell
This is a good resource on SCRUM, an agile method of development
Agile Software Development with Scrum
Agile Software Development with SCRUM by Ken Schwaber and Mike Beedle.