I discovered ratings by Outbrain and am loving it. Very simple to install on your blog, it puts an unobtrusive widget to allow readers to rate your posts. The software is still in beta stage so somethings aren’t easy to find on your own. You need to write to them to get your ratings report on their site. And you need to add an extra bit of code in the widget to make the most popular posts visible on your site (add var OB_showMP = true; as first line after script language tag).
But all in all, a great little widget to interact with readers.