Books? I don't really read any books on SEO but you can download many e-books with great SEO information. I have also found that by reading the most recent updates, blog and information at SEOMOZ, search engine land and search engine journal I can keep up with the latest trends and techniques far better. A book will get you going but SEO changes weekly and then again in heavy way on a monthly basis as well. The top SEO sites will keep you in the loop and learning more quickly than any book can.