Search Engine Optimisation books
Writing an article on SEO books is quite difficult. SEO (like most of the Internet) changes quite quickly, what is in favour one month could be bad practice suprisingly soon. Books are not updated as fast as this. Despite this, I have decided that many people like to read through the pages of a book rather than an up to the minute forum packed with geek speak.
Aaron Wall's comprehensive SEO Book manages to go into enough detail for some intermediate SEOs, but this is a great starter book with real in depth info that will help you acheive what you want with SEO and Online Marketing. More info on The SEO Book.
The most important search engine that will provide your site with most of its referred visits is Google and so a book to help you understand a bit more about this search engine is crucial. I have an old copy of Google Hacks which helped me figure out the importance of proper SEO as well as the flexibility of the Google API. This book can get quite technical at times, so I would ignore this book if I was from a traditional marketing background.
Search Engine Optimisation: An Hour A Day
A more rounded and less technical book is Search Engine Optimisation: An Hour A Day. This book is for those less interested in the technical side and more interested in the practical side of SEO. I would say this book is an excellent starter for new SEO's.
Search Engine Optimisation: An Hour A Day: http://www.amazon.com/Search-Engine-Optimization-Hour-Day/dp/0471787531/ref=pd_sxp_grid_i_2_1/104-9604579-8847162
Web Site Usability
As SEO is often measured by registrations or purchases (a process required from the user) usability becomes an important part of SEO. Without a usable website, you face losing customers you have attracted through SEO. This makes usability a concern for the budding SEO. Because of this I have linked to a usability book.
Web Site Usability: http://www.amazon.com/Web-Site-Usability-Handbook-Internet/dp/1584504692/ref=sr_1_17/104-9604579-8847162?ie=UTF8&s=books&qid=1185920742&sr=1-17