Some months ago I ran into some slides of Kelly Waters.
I see he has a promising eBook, now on sale for ten bucks.
I have checked his "agile principles" in the past and I have found his style quite enjoyable. He has a brief, well structured mindset, yet doesn't fall into the common mistake of writing some introduction in a agile-for-dummies minimalistic style. I really got useful ideas.
(please note, I am just convinced: I do not get any percentage :-)