1. This is a great article from Search Engine Land outlines some of the things you can do with your Google webmaster tools which can help with your SEO.
2. While technically not an article what Search Engineland has created in this periodic table of the elements for SEO ranking factors is pretty amazing and worth a study.
As they say on it “Search engine optimization — SEO — seems likes alchemy to the uninitiated. But there’s a science to it. Search engines reward pages with the right combination of ranking factors. ” This article from may help you to understand it better.
And to round out my list of 5 the last 3 are from SEOMOZ.org
3.The Seomoz social media checklist is not for total newbies but still worth a read by anyone interested in this aspect of SEO. http://www.seomoz.org/blog/the-social-media-marketers-seo-checklist
4. Another great article about the SEO favorite Title tag http://www.seomoz.org/learn-seo/title-tag
5. And finally a read on the use of the meta description tag -http://www.seomoz.org/learn-seo/meta-description