Awasete Yomitai I see this widget everywhere. In a nutshell, if you place the Awasete Yomitai widget on your site, it will start displaying other blogs that your readers are reading. It's great for the reader because it's a way to discover other related blogs.
When I first saw this blog widget it blew me away. The widget basically looks for negative words on your blog and starts fighting the word. Try the English version, on this page and pressing the 'fight' button. (It's pretty heavy so give it some time :) I thought this was a great promotion for Kendo magazine.
Gremz is a tree blog widget that you place into your blog. As you write posts, the tree starts to grow in over 3,000 different ways. If you stop writing, the tree dies. What I like about Gremz is that if your tree grows to an adult size, they will actually go and plant a real tree. It gives you an end goal to keep blogging. So far, they have planted over 3,800 trees all around the world.
Emonyu is twitter + blog widget with a huge focus on emotions. Through this web service and widget, you select illustrations (emoticons) and announce how you are feeling at the moment(happy, sad, frustrated...). It also closely tracks your emotions and provides an analysis. At the end of the month, you'll know your average emotion. Are you an angry person? Happy person? Moody?