I cant say that there is a "book" that I have seen as of late that would be worth buying on the subject of SEO. The thing with SEO in particular, is that the ideas and philosophies are so vast and varied, let alone the how different sites would require different aspects of SEO. What you do to a local business to develop leads would vary as compared to say a commerce site as an example.
I have been developing websites and traffic going back to the mid late 90's as much as the SEO environment has changed, for the most part it remains the same. My personal philosophies stem from the Google Florida Update ( November 2003 ) With the modern updates such as Penguin and Panda... you can see that Google laid the ground work way back then, and the current updates are simply defining ( or targeting ) those issues.
So with that.. in SEO I think it important to not only understand the past.. its changes and techniques, but where it is headed. I would suggest reading Bill Slawskis blog
http://www.seobythesea.com/. All this guy covers is the Patents that have been taken out by the assorted Search companies. Gives you a wicked crazy insight to into the mind of Google and the others. Not only what they are looking to develop and improve, but how they are going to go about making those changes.
This site:
http://www.seobook.com/blog is another crazy silly resource in terms of all things SEO. What I like about Aaron Walls blog is not only SEO in theory.. but he looks at the overall big picture of search and how it effects the web as a whole.
Looking at local search specifically you may want to look at
http://incomebully.com/ There are some really cool local search result breakdowns and you get a real good understanding of what makes local search tick.
To step back and get a bit of history on search engines specifically
http://infolab.stanford.edu/~backrub/google.html written by Sergey Brin and Lawrence Page gives you real good insight to the mechanics of a search engine... the better you understand how they work, the better you will be able to make it work for you.
The last bit of reading I would present is from no other than Google themselves:
https://support.google.com/webmasters/answer/35291 When it comes right down to it, for better or for worse Google is pretty dang transparent in what it is they expect from the SEO community.. what works, and what will get you nailed. The separating between white hat and black hat is trying to beat them, or joining them LOL
Aside from reading, nothing beats experience. I have suggested for years to learn SEO on your dime. Set up a Amazon affiliate site, get traffic and make sales. ( the reality here is SEO can make or break a wallet.. why not yours? ) I get paid well to do SEO, but stupid silly Amazon sites make far more month in and month out. The other site you should develop is YOUR site. Learn local search by developing traffic and leads for yourself. If you can do these things for yourself.. you can then venture out into the world of selling your SEO services with an amount of confidence and knowledge. Hope this helps!
Note to moderators: This post and the included links have been approved by WMS
