One option to get a bit further afield is County Parks. Since these Parks are generally outside City limits they are generally larger than City Parks and usually have more extensive trail systems. Given that I live in the South Bay I frequent the South Bay parks a lot. Again I'm pretty lucky that I can get to 4 or 5 of these in under 20 minutes.
For more info on these parks go to my hiking website at: www.HikingTheBayArea.weebly.com.