Check this out, a knol written by the editor of EcoHostReviews.com at Google.

http://knol.google.com/k/cyrus-patten/green-web-hosting/

Check these helpful resources out:

• http://www.treehugger.com/files/2007/05/plethora_of_opt.php
• http://davidherron.com/view/green-neutral-web-hosting
• http://en.wikipedia.org/wiki/Green_hosting