Adsense is by far the best, I've tried adbrite, and rockyouads in the past but by my experience i suggest the adsense.
There's a UK-based service called Message Space http://www.messagespace.co.uk/
They have a limited demographic, however.
http://bethatwriter.blogspot.com Free online writing course and resource for writers
http://thats-business.blogspot.com/ Online business magazine