According to her fans (see Why I Love Beth's Blog), Beth's Blog provides "deep analysis of social media campaigns, trends, and uses" along with case studies.
Blog and business site for Nancy White, a leader in "online group facilitation of distributed work, learning and community groups." The site includes both a blog that speaks to White's current work and interests, and also resources for online communities and related work.
By Seth Godin. His self-described topics of interest are "post-industrial revolution, the way ideas spread, marketing, quitting, leadership and most of all, changing everything."