So there are many large organisations out there whom are leading the way of how to write and execute a Social Media Policy (SMP).
There are also a number of databases and registers of the most common and public ally accessible Social Media Policies.
Social Media Governance, which has 163 policies listed and where you can upload your own Social Media Policy - http://socialmediagovernance.com/policies.php
123 Social Media also have a collection, a point of difference comes in with the Barack Obama case here - http://123socialmedia.com/2009/01/23/social-media-policy-examples/
Compliance Building also have a collection, with 236 policies currently listed - http://www.compliancebuilding.com/about/publications/social-media-policies/
You can also find a free tool online which allows you to create a customized Social Media Policy for your business.