My girls LOVE Ranger Rick magazine and have been reading it for years.
Other good scientific magazines would be Odessey, Zoobooks, Muse, Ask, and Faces. All add free.
Other books:
DK & Eyewitness Animal books--- a whole series on broader topics (Mammals, Animals, etc and also specific ones like Birds, Dinosaurs, Dogs, Apes, etc) GREAT pictures and information
Magic School Bus & supplemental Magic TreeHouse books, Biographies on famous scientists like Jane Goodall, Dian Fossey, etc or even the animals themselves : KoKo, Balto, etc.
