I just picked up ScrumBan from Cory Ladas. Very thoughtful and interesting read. Cory does an excellent job describing lean principles and offers some examples that are very easy to understand. Check out Cory's blog. There we a few comments he made that I don't neseccarily agree with - for instance that XP is a derivation of V-Model. This was a bit dismissive of the revelolutionary work the Kent Beck did on XP! But again, if you into agile and want to learn about lean check out ScrumBan.