Related book or journal article suggestions are given in their respective chapters. Web resource suggestions include:
Broad Link or Article Sites
www.agilealliance.com Collects many articles specifically related to agile methods, plus links.
www.cetus-links.org The Cetus Links site has specialized for years in object technology (OT). Under "OO Project Management OOA/D Methods" it has many links to iterative and agile methods, even though they are not directly related to OT.
www.bradapp.net Brad Appleton maintains a large collection of links on software engineering, including iterative methods.
www.iturls.com The Chinese front page links to an English version, with a search engine referencing iterative and agile articles.
More Specific Sites
c2.com/cgi/wiki?FindPage This important, vast Wiki site was the home ground where many of the agile leaders (and design pattern leaders) held their original discussions on XP and other agile methods.
www.extremeprogramming.org Don Wells' (an early XP leader) introduction to XP.
www.xprogramming.com Ron Jeffries' (an early XP leader) introduction to XP.
www.agilemodeling.com Scott Ambler's site contains many articles related to agile modeling practices.
sunset.usc.edu Associated with the work of Dr. Barry Boehm, a long-time researcher into iterative (e.g., Spiral) methods. Articles related to iterative methods.
www.cutter.com Cutter's site has an Agile Project Management specialty area.
www.martinfowler.com Martin Fowler is an early agile methods thought leader (XP method). Articles and links.
www.jimhighsmith.com Jim Highsmith is an early agile methods thought leader (Adaptive Software Development method). Articles and links.
alistair.cockburn.us Alistair Cockburn is an early agile methods thought leader (Crystal methods). Articles and links.
www.controlchaos.com Ken Schwaber is an early agile methods thought leader (Scrum method). Articles and links.
jeffsutherland.com Jeff Sutherland is an early agile methods thought leader (Scrum method). Articles and links.
www.gilb.com Tom Gilb is one of the very earliest iterative and evolutionary thought leaders (Evo method). Articles and links.
www.craiglarman.com My site. Articles and links.
www.objectmentor.com Company led by Robert C. Martin, an early agile thought leader (XP related). Articles and links.
www.nebulon.com Company led by Jeff De Luca, an early agile thought leader (Feature-Driven Development method). Articles and links.
www.dsdm.org Official site for the DSDM method.
www.rational.com Official site for the Rational Unified Process (RUP) iterative method.
name.case.unibz.it Network for Agile Methodologies Experience (NAME). A European site that describes research into agile methods, and with links to other sites.