Check out the American Colleges and Universities President's Climate Commitment. It is a collection of universities whose presidents have signed commitments to reduce or eliminate carbon emissions in a certain timespan. Member universities must:
- Complete an emissions inventory.
- Within two years, set a target date and interim milestones for becoming climate neutral.
- Take immediate steps to reduce greenhouse gas emissions by choosing from a list of short-term actions.
- Integrate sustainability into the curriculum and make it part of the educational experience.
- Make the action plan, inventory and progress reports publicly available.
As of right now, 665 universities have signed the commitment, and are in various stages of the process. Universities have some discretion in terms of how and what they count for emissions, but the program does provide certain guidelines and requirements.
With nearly 700 schools on the list, it would be difficult to say which one is the furthest along, but if you're interested in finding more information, or seeing how to get something like this started at your school, there's a lot more information on their website.
Another measurement is renewable energy purchasing. The Environmental Protection Agency maintains a list of the top 20 college and university purchasers of renewable energy in the US.
(The list is ranked by total renewable purchases, although percent of energy from renewable resources is also listed. I would personally prefer to see it listed by percent, not by sheer quantity, since it doesn't seem right to praise an institution for using a lot of renewable energy if their overall energy consumption is very high and they are still using a lot of conventional energy sources.)
Right now, The University of Pennsylvania is leading in annual "green power usage", with about 200,000,000 kWh (but only 48% of their energy is "green"). The university with the largest amount of "green" power usage that also has 100% "green" power usage is Carnegie Mellon University (116,000,000 kWh), followed by Georgetown University (113,000,000 kWh) and Oregon State University (95,000,000 kWh).