Above all learning should be fun. Here are a few links to things I like dealing with nature and science.
Bird and Moon
Wonderfully drawn nature/naturalist cartoons. Informative and humorous at the same time.
A meteor impact calculator from Perdue University. Kinda fun to play with.
What a reality show should be: a group of scientists working together with limited resources to solve various puzzles. Interesting, fun, and educational. This BBC series ran from 2000 to 2005 and had 6 seasons, PBS only showed 4 seasons.
Interactive wildlife learning flash game by PBS KIDS. It’s an animated adventure with games and environmental habitats your character wanders through, gaining animal abilities as you go. There is a teacher’s portion as well with optional lesson plans for instructors to use or modify.