Reporting standards: GRI
The Global Reporting Initiative tries to set a standard for business reporting about sustainability results. It is already adapted by many companies.
The global reporting initiative serves as a good way to compare companies on how they perform on sustainability issues. What I like about GRI reports, is that you can clearly see what improvements companies are making, for example expressed in emission impact, but it's also a good tool to see within a company how well you are doing and where you can find more ways to improve.
Screenshot of GRI website