Try the Scholastic web site. They have a lot of terrific resources. I'm not sure if it's online, but Highlights magazine is old but terrific. Time for Kids is also fun. Check with National Geographic, too. Beautiful pictures, interesting subjects.

Teacherlady is right. You can also try students' digest. ( http://www.studentsdigest.org/ )

This magazine is a 21st century resource for inculcating values and good habits, anf it aims to promote values and ethics in an entertaining and engaging way.