Technorati

From the site:

"Technorati is the leading monitor of the world of weblogs. Technorati is a real-time search engine that is the largest source of fresh information about the global and local conversations going on all across the Web. Technorati allows you to find out what people are saying about you, your company, your products, your competitors, your politics and, other areas of interest, on the Internet in real time."