Kind of old news now but The Times have published the 50 best business blogs. They cover technology, media & marketing, and other industry sectors. So there's some obvious ones in there but a couple that I didn't know about. One in particular was the Freakonomics blog which is written primarily by the two author's of the well know book - Stephen D. Levitt and Stephen J. Dubner and provides some really interesting insight into the correlation between seemingly unrelated statisitics.
Now most people in the free world have at the very least heard of the book. If you haven't read it I would REALLY encourage you to pick up a copy on Amazon. If you're a data geek like me you'll really enjoy the read.
Oh and here are 5 blogs I read everyday...in no particular order.