Muse is not an inexpensive magazine (over $30/year), but my gifted D absolutely LOVED it. She was about 8 or 9 when we started getting it, and we got it for several years. It was a small price to pay for the information and joy she got from it.

http://www.cricketmag.com/ProductDetail.asp?pid=12

If it is too pricey, see if you can talk your local library into subscribing.