Holly Molly - no secrets anymore Rated 5 out of 5 stars
I'm not an expert at this stuff and maybe there is other good stuff out there - but this gives an amazing breakdown of a site.
I feel like a black hat guy with access to secret stuff. In essence all you want to know is here.
Great for analysing other sites and seeing what others see about your own.
A great tool for more in depth SEO research.