Technorati Link Count Widget
Technorati is the go-to search engine for bloggers. It shows you every single link to posts made about you in other blogs, along with an authority rank that tells you how important that blog is. This widget enables you to display in real-time the number of links/discussions happening about your posts, which they call "reactions." Of course, your blog should be very active in order for this widget to be meaningful. The site has lots of other interesting widgets too.