My three books on agile made this list of “The Top 100 Agile Books” by Jurgen Appelo. He used an objective method of ranking books based on Amazon.com and GoodRead.com quality ratings and popularity. His blog explains the approach. Uncle Bob Martin and I were each fortunate enough to have two books in the top ten. Just about all the books on the list are worth reading so pick up a few of them if you're looking for something good to read.