Hi, you can refer to the AA1000 framework and to its related standards basicly usable for assurance statements or for stakeholder engagement. In addiction you could use also the Copenaghen Charter, mostly linked to the reporting process.
There are many NGOs who have their own substantive and reflexive standards (and regulatory instruments).
You may look into one of my academic contributions, entitled: Valuing Non Financial Performance and Sustainability Reporting which will be published very soon! :)