Here are a few cool blog tools I've come across while researching Chapter 15 of my upcoming book on blogging:
Ping-o-matic - Lets dozens of services know you've updated your site and increases traffic to your blog.
Blogbox - offers a variety of easy-to-add features for your blog.
Blog Tricks - a lot of nifty blog add-ons like a referrer list you can post on your blog.
Blogdex - an MIT project tracking the "diffusion of information through the weblog community."