I like click (younger) and muse (older) published by the same people who do spider/cricket, etc. except these are non-fiction mags.
Click is great for "unit study" type stuf with preschool/elementary since each issue is on a theme. and they have a web site for parents with related books/activities etc.www.clickforparents.com
It's a bit pricey but there are no ads. (excpet order cards for their other mags)