From the U.S. Department of Agriculture, this site offers a wide range of agricultural images, many of which support the investigation of seeds and germination.
This pretty site from the Spencer Entomological Museum at the University of British Columbia offers a useful glossary of terms (click on "Insect Lore") and some beautiful images in the "Bug of the Month" section.
The name pretty much says it all. This site offers a huge collection of animal imagesjust search by name. They also provide animal sounds, animated movies, and clip art.