I'm getting my son a subscription to Scientific American. We really love that magazine!
Sometimes I've found that it takes a theory and makes it sound like fact - which is something easy to do, but important to be aware of. But it does have really fascinating, easy-to-read articles.
Also, my husband brought home a 1955 physics book from his parent's house - "Visualizing Physics" - I have learned so much from that book! I plan to read the entire thing with my older children.