technorati

The website http://www.technorati.com/ tends to cover a very wide range of topics under the sky. It has to use a lot of tags to do so.
I find the 'popular' tag very useful, and also the statistics provided in 'blogosphere'.

Here is a comment about technorati from another blogger:
Technorati is a real-time search engine that keeps track of what is going on in the blogosphere — the world of weblogs. Technorati tracks the number of links, and the perceived relevance of blogs, as well as the real-time nature of blogging.