Semify's Web Grader is unique in that it gives you detail about offsite SEO -- your backlinks. And, you can plug-in your competitor's URL and see how you compare.
Onsite SEO is also an important metric. According to SEOMoz, 30% of rankings can be attributed to onsite SEO and 70% to offsite SEO, or link building. This web grader gives you the critical offsite SEO data.
Watch this video for a quick SEO tutorial on how to use the Semify Web Grader.