If "environmentally friendly" is near the top of the list on your RFP, you might want to take a look at EcoTrotters, a site that hopes to get travelers to write environmental reviews of hotels they stay at. There aren't a lot of places in the database yet, but I'm sure it's just a matter of time. It also has some decent content, including this article on how to tell if your hotel is really green.
While it's not on the official form for hotel reviews by and for meeting planners at the Meetings Collaborative, I'm sure that's something that more planners will be commenting about as the movement to green meetings gains momentum.
(Thanks to Hotel Chatter for the pointer to EcoTrotters.)