We have a subscription to Kids Discover magazine also and love it (no ads)! They have other lesson plans and resources for parents and teachers there too.
For free human biology and science DVDs and Cd's, go to the Howard Hughes Medical Institute.
They also have some printed materials free that they ship as well.
Check out their Cool Science link for interactive educational help for children of all ages.
I'm always thrilled to find quality resources on the web and will pass them on when I do!