Sutro Project / Muni
Combining with BART for a poor man's subway system, the Muni (officially "Muni Metro") light rail works well for some routes. The vehicles run below ground along the Market St corridor and otherwise operate on the roads.
Muni Buses cover much more ground, more slowly, and most bus shelters have a map of the whole Muni system, along with somewhat reliable real-time info - also available here.
Muni offers a variety of passes, accepts Clipper cards, and a 7-day pass is included with CityPass.
Dogs may ride Muni too! They must pay the fare and not during rush hours, unless they're service animals.
Website: http://www.sfmta.com/cms/home/sfmta.php
Wikipedia: http://en.wikipedia.org/wiki/Muni_Metro
