I have been reviewing a few of them recently for the book, including Google's blog search, Technorati, IceRocket, and BlogPulse, but may favourite at the moment is BlogScope.
I like the advanced search options and I like the extras.
For example, when I searched "Climate Change" it generated 403K results with at least some influence. It also suggested the following ten words were the most associated terms
This search can be seen here although, your results will be a newer than mine of course.
I also really like the popularity curve, see image below.
Click here to see the popularity curve live on the site.
So, what is your favourite blog search tool?