I subscribe to 2. Water Gardening, plus I also purchase a few at the market every now and then.
My second one is Fine Gardening this is the "Cream of the Crop" It is the best magazine on the market. Each month it highlights certain plants. They are the most informative articles I have ever read in a magazine.
So far two thumbs up for Fine Gardening, it really is an excellent magazine.
Here's a link to Epinions website, the section dealing with Garden Magazine reviews. They have 31 magazines listed, you might find something there that sounds just right for you.