Widgets are a great way to add third party content to your site. Spotback is a new one in this arena which works great for rating the posts. I had added the widget some time back and ever since it has been working great for me! It allows users to rate your site and tag them to use in future. Moreover, they can easily read posts which have been rated high by viewing the recommendations or the ones recommended by the site owner. You can also view the tagged items. Simply a lot of good nice features in a small widget which adds a lot of interactivity for the end users! It is still in beta, so one can hope to see more features coming with time!