This is an interesting blog post by Google: http://googlewebmastercentral.blogspot.com/2010/03/googles-seo-report-card.html
Its helpful to see how Google evaluates its own SEO and what criteria it uses.
Google has also posted a very helpful guide to SEO here: http://googlewebmastercentral.blogspot.com/2008/11/googles-seo-starter-guide.html