Shout out to Amnesty International - check out their brilliant use of video, pictures, blogs and many other apps on their Facebook page.
Pay special attention to their wall posts - the use of stories to personalize the issues, the use of questions to encourage participation. These are good tactics to keep in mind when you creating your own social media campaign.
If you have achieved enough mass, you can test each story and each question in your social media campaign and use the most popular in your other campaigns to increase the chances for success. If you don't have the mass yet, learn from Amnesty and other successful social media organizations by visiting their sites.