Here's a sampling of the best in my RSS reader:

• Scott Aaronson, theoretical computer science/physics
• Tyler Cowen, economics, Cowen is good about sharing surprising info
• Lambda the Ultimate, programming language theory
• John Baez, "from math to physics to earth science and biology, computer science and the technologies of today and tomorrow," plus stuff on catastrophic risk w.r.t. climate change.
• Jeremy Kun, computer science mostly
• The n-Category Cafe, "A group blog on math, physics and philosophy"
• Andrew Gelman, pointing out bad statistics in social science. More than once, I've revised my beliefs about some study months later when he points out a failure to replicate or other problem.
• Timothy Gowers, math, analysis I stuff recently, mostly over my head
• Terry Tao, math, number theory, mostly over my head
• matthen, math visualizations
• Gödel’s Lost Letter, theoretical computer science, complexity theory, often funny
• MIRI blog, interviews, research recaps, computer sciencey
• Overcoming Bias, X isn't about Y
• Dart Throwing Chimp, global politics
• Carl Shulman, effective altruism, thoughtful analysis
• Saturday Morning Breakfast Cereal, webcomic
• So Your Life is Meaningless, webcomic
• XKCD, webcomic
• hbd* chick, population genetics, star wars, emoticons
• Unqualified Reservations, neoreactionary, questioning everything since the enlightenment
• Yvain, psychology, rationality, relationships
• Ben Kuhn, effective altruism
• Katja Grace, rationality
• Brienne Strohl, rationality
• And finally my blog, I try to share surprising information, cogsci/relationships/computer science/math

gwern posts on google+ and Kaj Sotala posts interesting stuff on Facebook. I also subscribe to a number of journal's table of contents via this site to keep up with research and some stuff on arxiv.