Shaun, aka Hobo, has released a 157 page PDF guide on SEO. You can download the book over here.
There are many SEO books out there, some free, some at a price. I would list some that I recommend, but I honestly don't want to leave any out. So I'll just list a few, but please don't be insulted if I don't list yours.
Those are just a few and now we have this new one.
Forum discussion at Sphinn.