Here is a MASSIVE list of potential reading sources, most are available online, but I have included a listing of helpful books as well. Bookmark the post so you can test out the different sources to see which ones you like best. The sources were not designed to give practice to GMAT students hoping to improve their RC, so you may have to look around a bit to find texts that are similar to the GMAT (i.e. look in the research section of the Harvard Magazine).
Websites
Harvard MagazineUniversity of Chicago MagazineMIT Technology Review Smithsonian Magazine The Atlantic Slate The New York Review of Books The New York Times Book Review (10 free articles per month for entire NY Times)
NASA News Scientific AmericanPLOS (Public Library of Science) Popular Science Psychology Today The SocjournalArts & Letters DailyBooks
Thinking, Fast and Slow, Daniel Kahneman
Guns, Germs, & Steel: The Fate of Human Societies, Jared Diamond
A Short History of Nearly Everything, Bill Bryson
This Will Make You Smarter: 150 New Scientific Concepts to Improve Your Thinking, John Brockman
Art History: The Basics, Diana Newell H America’s Constitution, Akhil Reed Amar
KW