Seth Godin keeps a running total, based on Alexa  data.

On a related note, Search Engine Journal has an excellent article about Yahoo’s acquisition of MyBlogLog:

“MyBlogLog is a hybrid between a blog analytics solution and a social networking environment which has recently swept the blogging world by storm. A ‘MySpace for bloggers’, MyBlogLog lets registered members congregate around communities set up by those members or the blog owners themselves“

MyBlogLog was #47 on Seths chart.