Biome Worlds Project
A few sites for Biome research:
This site gives brief summaries of the basics of most of the biomes as choices from this project.
University of California Museum of Paleontology - The World's Biomes
This site, produced through UC Berkeley, has a wide range of information on the major biome types and breaks down the biomes into sub-categories quite clearly.
This site has some good information on the subcategories of biomes, and has nice FAQ and links pages that are helpful.
A nice, clear site with plenty of information without going too much into detail.
Center for Educational Technology, Biomes Module
Visit the "Earth Floor" and check out the variety of biomes we have there. A good site for lots of information.