Russell Brown has created a plugin that generates a sitemap.xml file for your blog. This file makes it easier for Google and other search engines to index your website.
Read more and download at Russell's blog.
Josh has created a tag that you can add to your skin to output ads provided by ShoppingAds. Read more at Josh's post.
I agree with him that plugins are less intrusive than tags, since you don't have to change your theme files. While I cannot anticipate where people would like to add ads in the html, I am planning to add a template event to the bottom of the post and make it easier to add "pods" to the blog sidebar. I hope that that will, at least partially, solve that problem.
Josh has created a plugin to embed a Blip.tv video into your posts. Read more at Josh's blog.
I am thinking that we should have a single plugin to output any of the popular video sites... :)