Many test prep courses encourage reading magazines or journals that are a little more scholarly - The New Yorker, The Economist - that one sciency one I can't think of the name - oh man it's so on the tip of my tongue -
Anyway, I think more important than what you read is how you read - make sure you are always paraphrasing to yourself as you go, try to figure out the point of the article, whose point of view it is, is it an argument about something, or just something explicative. I have taught strategies for the Verbal section, and it's really a matter of being very aware of what you're reading. You want to make sure you "get" what you just read, no matter what it was. And do a lot of practice tests!
Scientific America! Thank you.