I am a seasoned SEO and have not read much on the subject, but i decided to buy some books to read in my spare time. Here is what I recently bought:
# 1 of: Simpleology: The Simple Science of Getting What You Want
# 1 of: The Tipping Point: How Little Things Can Make a Big Difference
# 1 of: Professional Search Engine Optimization with PHP: A Developer's Guide to SEO
# 1 of: Radically Transparent: Monitoring and Managing
# 1 of: Professional Search Engine Optimization with ASP.NET: A Developer's Guide to SEO (Wrox Professional Guides)
# 1 of: Blink: The Power of Thinking Without Thinking