Check out the promising new magazine, Babel, written by linguists for non-specialists. I’ve read a bit of the first issue and I thought it was at a fairly nice level–new ideas if you haven’t had any linguistics classes at all; not too challenging if you have, but still plenty of interest. There are some great people on board. I wouldn’t have heard of it if it hadn’t been for David Crystal’s blog post about it, due to being fairly absent from Twitter. (Thank goodness for Google Reader.)
For now, you can read the first issue of Babel online or download it. It has a very wide range of topics, including an article on xenolinguistics from someone who definitely knows his sf.
They were just looking for book reviewers via their Twitter account, too, if you’re interested (I probably don’t have quite enough of a linguistics background, alas, and there’s that appalling parentheses addiction, too).