[Ambler and Jeffries 2002] Ambler, Scott W., Jeffries, Ron, Agile Modeling, Wiley, 2002.
This is the best book I've seen on the topic of lightweight documentation. It is packed with ideas on how to capture requirements, specifications, design, etc.
[Beck 2004] Beck, Kent, Extreme Programming Explained, 2nd Edition, Addison-Wesley, 2004.
Kent Beck does an excellent job of introducing the motivation behind continuous integration, nightly builds, and prototypes. The Extreme Programming literature is in general filled with many useful ideas and practices.
[Hunt and Thomas 2000] Hunt, Andrew and Thomas, David, The Pragmatic Programmer, Addison Wesley, 2000.
This is an excellent book for software developers, and I highly recommend it. Some of the practices described in this book are derived from the pragmatic programmer.