I don't use any at the moment. However, at one time I was using the Moz toolbar, and I think the Google PR toolbar. I can't really remember. Who has used those? Well, Google PR is obsolete these days. Either it's a secret or diminished.
I was using multiple SEO tool bars in the past, SEO Quake was my favorite. However, later I stopped using these tool bars because they slowed my browser. It is easy to analyze the site you visit if you use SEO tool bars in your browsers, I might start using SEO tool bars again.