You could try the library and see what magazines they have in kids and adult magazines. It depends on what your child is interested in and also his reading level.

We like Odyssey, Dig and Cobblestone (by Cricket, they also make Muse)
Also look at trade magazines or building magazines in the adult section if your child is interested in something specific, like Engineering.

At second grade, we all still liked Highlights and Ranger Rick and National Geo kids.

Magazine subscriptions make great gifts!