I F*ing Love Science: http://www.iflscience.com/ and
The blogs at Popular Science magazine
The blogs at Scientific American (magazine). Including the Urban Scientist: A hip hop maven blogs on urban ecology, evolutionary biology & diversity in the sciences and Cross-check: Critical views of science in the news
From Teachthought: A 100 scientists on Twitter.
Business Insider: 40 scientists to follow on social media .
Dodo: Conservationists on Twitter.
The American Geophysical Union blogosphere.