I'm with Perky.
I usually compare sites with my competitors. The last site that I focused on SEO I used an IBP program (not sure what the software was called, SEO related though). It worked very well and gave me a chance to do my SEO and see how well I'd rank in today's standings based on changes. It also offered me a wealth of info on changes that should be made (including the weight of current backlinks) to improve on key phrases.