Michael Schaefer's Deep Blog is a useful tool and worth checking out. It is a quick and simple portal to top blogs in many different categories -- a place where blogs are easily found and accessed.
Here's what Michael says: "Since we like diversity, this site is categorized so that tech blog readers might be encouraged to easily check out topnotch political blogs, or religious blog readers may quickly find contemporary cultural blogs and vice versa -- a place where the guys and gals who helped invent and nurture the blogosphere are highlighted and where the big search directories for news and blogs can be accessed for current information."
Here are the two ways that I use Deep Blog:
1. I am often asked to comment in MSM articles (magazine, newspaper, radio, TV). Often the reporter is with a local publication or a trade publication. Before the interview, I check out Deep Blog and scan the popular blogs in the space so I can mention an appropriate blog
2. When I speak at conferences and company events, I like to have a screen shot or two of the popular blogs in that industry. Deep Blog helps me to quickly locate something.
No, it isn't perfect, but neither are other ways to find blogs. But used together with a good blog search engine like IceRocket, Deep Blog is very useful.