I would like to find bloggers who speak to my target market, and who might mention my business and therefore drive name recognition and search engine optimization for my website. Any suggestions on how to go about identifying the most popular bloggers in any given market niche, and how to find any actual data regarding their level of popularity?
Technorati has some data, but you might consider that the bigger they are the less likely they are to respond to a cold email asking for promotion.
You can also use compete.com to get traffic results. It doesn't show data for sites with a small amount of traffic, but you are probably not looking for them anyway!
I can't answer your question, but I would suggest you also try posting your question on inbound.org. It's a site like this one, but its focus is inbound marketing. The site is still really new, so there aren't a lot of users yet, but it's worth a shot.