What a great question. I have been researching Search engine optimization for about 3 months now.
Actually, keywords are pointless now for Google searches. Google is the #1 search engine, plus does the searches for Yahoo (thought it probably won't take long since it's recent purchase of
overture ) Speaking of overture, click on that link for a "search term suggestion tool". Optimize your pages for the top keywords. When I say optimize, I mean make sure the title of the page, and the content contain the top keywords, but make sure each page focuses on a different search word.
The first directory you should get registered in is dmoz.org Independent directory that Google uses. Very important.
Books to buy:
Google Hacks published by O'Reilly, authored by Tara Calishain & Rael Dornfest. The only book about Google at this time. Even google approved. Focuses on some subjects such as developer tools, that you may have no interest in, but it is still interesting.
Use
Bruce Clay's website to analyze your website for you. He has a lot of great tools and tips. He suggests some other books as well.
Visit
Site Point Forums for a lot of information on search engine optimization, plus they will analyze your website for you. Great community.
I could type for days on this, but this is the outlined form of everything. If you want to know more on anything above, let me know.