Seth Godin's riffs on marketing, respect, and the ways ideas spread.
http://sethgodin.typepad.com/

Another great marketing/social media blog.
http://www.techcrunch.com

Creative Advertising Archive & Community
http://adsoftheworld.com/

http://www.adrants.com/

ProBlogger Blog Tips - Make Money Online.
http://www.problogger.net/

Copywriting advice for bloggers and online marketers.
http://www.copyblogger.com/

AdLand, the beyond-a-blog, commercial-laden delirium of heaven and hell for advertising addicts around the world, gossips about advertising stunts and ...
http://commercial-archive.com/

Andy Beal writes on search and internet marketing.
http://www.marketingpilgrim.com/

Quantitative analysis of web traffic, by Compete, Inc.
http://blog.compete.com/

The most visited blog in the world, need I say more
http://www.mashable.com

A blog about the contrast between the excitement of digital and its sometime soullessness
http://www.ale2.co.uk

http://www.whatsnextblog.com/

http://searchengineland.com/

http://www.davidairey.com/