Some useful links

Mary and Tom Poppendieck's site
Mary and Tom (from Eden Prairie MN) wrote some great books on how to apply the Japanese manufacturing idea of Lean to software development.  I find their methods more useful than any Scrum, XP or any other methodology out there.

Agile Manifesto
These are the ones who bucked the waterfall model and started a revolution.

Running Agile
Christophe Louvion's blog on Agile with a who's who of Lean and Agile leaders

Wikipedia on Agile
Wikipedia is a good repository for all information these day. 

Joel on Software
This is not technically Lean or Agile, but this guy seems to understand what goes wrong with projects and how you can fix it.

userStories
Mike Cohn maintains a list of tools to support Agile and Scrum tools. 

Tom Peplow's Blog
Burndown charts don't tell you if the software actually works.