The Atlantic Monthly - A wide variety of different subjects, but especially strong on economy, American history, politics and urban planning.
Parents Monthly - A favourite magazine and website for my friends who have kids.
The New Internationalist - A British magazine dedicated to topics about global development. If you enjoy thought-provoking articles about the world at large, you'll probably enjoy NI. It's also an exceptionally good source of vocabulary for people who need vocabulary that focuses on international relations and economics.
Some of you will ask why I didn't include "The New York Times". Unfortunately, the "Times" has adopted a new policy that only gives you twenty free articles per month, and while most students won't read more than twenty articles, I think it's a good reason to start looking elsewhere for things to read.