For what it's worth (FWIW) – I just ran across this Blog Index (Alpha). Not sure when this was introduced (perhaps vintage 2008?). I don't fully understand the scope and rankings yet, but I find the discovery interesting given my time away from actively being involved in the corporate blogging space. Notes to self: one consulting firm (Accenture) on the list at #18 of 48, heavy tech in top 10, and mixed industries in top 30.
Update (2/7/09): Dr. Urs (CTO associated with the technology) contacted me to inform me that the tool is still in Alpha phase. More info on how the tool works can be found here. Registration and accounts can be obtained here. The is also a Twitter stream covering tool improvements, etc.