Martin Missfeldt of TagSeoBlog.com did a really nice piece on Google search ranking and what factors into the ranking.
From Tag Seo Blog :
There is a lot of discussion around about Google’s search ranking factors. Sometimes these factors are described as a list. They try to rank the factors by importance. In my eyes this doesn’t make sense. The Google algorithm gets more and more complicated. The main question is not: which signals are ranking-factors. But it is: how are they connected and related.What are “main factors” that are build by addition of a lot of single signals?