MyBlogLog appeared in the sidebar of my previous blog (and it’s still there). It doesn’t appear here, partly because of MBL itself, partly because of my sparse sidebar policy.
If I were looking for social sidebar stuff, I’d give Explode a try. It provides a JavaScript widget, which can’t be used here at WordPress.com (or at MySpace or Vox or…). It also provides the thing you see in this post. For further discussion, see the post at TechCrunch.