We get asked that question a lot. Just how do you get information on a blog. It is of course useful to understand what goals you should be looking at. One should always be realistic what they can achieve given their niche. Obviously entertainment rags (eg Perez Hilton), techno-geek sites (Techcrunch) and big news aggregation (Huffington Post) sites get big rankings so they are difficult to compete with, but it is very possible to get good traffic in your own area such as opinion on politics and the law.
The is one reliable source and that is Technorati. As you can see above Blogcritics, which we write for from time to time, has a weekly page view of 1/2 million so 2 million per month. You can find it at http://beta.technorati.com.
Head over and wander around, it is very enlightening.