While working with the fine folks at Climate Neutral to measure, offset, and reduce our carbon emissions we brainstormed 38 initiatives we could pursue to help reverse climate change. One that we elected to do right away was opt in for "SuperGreen" electricity supply via the San Francisco Public Utilities Commission (CRM: 010005759). This ensures that our electricity comes from 100% renewable sources as certified by Green-e, a program of the Center for Resource Solutions.
If you work in a business in SF, you can do the same via this CleanPowerSF link:
They have residential programs as well: