There are so many web sites on zoology and botany that rather than attempting to list specific ones, below are mainly sites that gather high-quality links to specific web sites.
The diversity of all organisms, living and extinct. Their evolution, phylogeny, and characteristics. Search by keyword or use the graphics to follow the tree's branches. Lots of images.
This site describes itself as "an ambitious project to organize and make available via the Internet virtually all information about life present on Earth." They plan to have a page on each organism on earth.
Considered the most complete and up-to-date list of threatened plants and animals. Entries are rated by how endangered they are. From the International Union for Conservation of Nature and Natural Resources. (The above entry is better for a general overview of the topic.)
Beautiful photos and basic information about insects and spiders. You can browse by type of bug or use the table of contents for an alphabetical listing.
Information from the US Dept. of Agriculture on organic and sustainable farming practices. Covers growing crops, pest management, water management, and more.