Biomes of the World, Freshwater and Marine Ecosystems Very well organized information.
Microbe Zoo - Discover the world of microbes in the environment.

Boreal Forest
Mammals - by Animal Tracks Den - index  easy to use - good information - North American mammals
Mammals of the Boreal Forests - Canadian - Excellent
Mammals of Northwestern Ontario's Boreal Forests

Rainforest
Rainforest Animals -very thorough presentation of animals, pictures...
Rainforest Action Network  Wide range of useful information on species found there.

Tundra
Tundra - very good information with many links of explanation.