First of all don’t forget that the search engine optimization exists only because the existence of the search engines. The main reading must be centered on the SE documentation and blogs.
I made a short list of basic resources for SEO beginners.
http://www.google.com/webmasters/ Google Webmaster Central. Every SEO enthusiast must start from here.
http://help.yahoo.com/l/us/yahoo/search/webpublishers/ - Yahoo Search Help, if you want good ranking in Yahoo, this step is important.
http://googleblog.blogspot.com/ - Official Google Blog
http://googlewebmastercentral.blogspot.com/ - Google news for webmasters
Anyway if you are interested in ranking good in other search engine the fist place to stop and ask questions is its documentation, online help or blog.