The Daily Kos is the highest ranked political blog of any stripe, registering more than 500,000 unique hits per day. It has more than 50,000 registered users who post a collective 275-300 diaries per day. Unquestionably it has changed the nature of political dialog in this country. All in three years. Thank you, Markos.
Interesting analysis on the stagnation of the right-wing blogosphere here.