HubSpot's Website Grader is a web-based tool which analyses and scores your website against a number of criteria, and provides you with a report card flagging areas you may wish to improve. By filling out a web form which asks for your URL, keywords related to your blog and optionally any websites you compete against, it generates a report on your site. You need to supply an email address as it mails the link to you.
The score it generates grades your website against a number of things including website traffic, search engine optimisation, social popularity (via social bookmarking and sites like Digg) and a wide range of other factors. It also provides some very basic advice on how you can improve your website's performance.
One thing which tickled me is that it rated Lifehacker's readability as "advanced/doctoral" level. I had no idea we were so rarified! I'd better duck back to uni and get that PhD. :)
What's Your Website Score? [Dipping into the Blogpond]