Cal Newport is the author of a myriad of books on student learning and advice (How to Become a Straight-A Student being one of them). He’s a CS professor at Georgetown University, and his website has an extensive amount of efficient tactics people can implement in their daily routines.
Scott Young is an efficiency guru, but mostly leans towards learning efficiency. This is a guy who undertook his own self-created “MIT Challenge,” in which he tried to learn MIT’s four-year undergraduate computer science curriculum in twelve months using MIT’s online course materials. He was successful in passing all his courses, and you can read more about the challenge here.
You can’t really talk about efficiency without mentioning Tim Ferriss. The man who coined the term “lifestyle design” epitomizes efficiency in his pursuits; he’s someone who really practices what he preaches. I don’t agree with all his methods, but it’s impossible to argue with his impact on the “efficiency” community.
Chris Guillebeau is a writer dedicated to spreading his social movement, “The Art of Non-Conformity.” He writes a bunch about his traveling adventures (he’s visited all 193 countries in the world) and how to live a remarkable life. Check out his books here (they’re all fantastic and digestible) and his life manifestos here.