I would also highly recommend reading Mike Grehan's "
Search Engine Marketing: A best practive Guide". It's currently in a second edition, but the third edition is due out very very soon. It really goes into the algorithms that search engines use, and general advanced SEO theory based on the maths. Great stuff, and kept simple for the layman, too.
I put up a review here:
http://www.platinax.co.uk/seo/review...h-engine-book/
and really do recommend any commercial SEO's to read it - if they haven't alerady.
