I sometimes sit in with a San Francisco band called Banda Sin Nombre, which plays a combination of folk and Latin and bluegrass music. They often busk along Valencia Street down in the Mission.
Here's a video of us playing at the San Francisco Free Folk Festival.
I got off a good solo on "Sitting On Top Of The World" in this clip.
Also at the Free Folk Fest I jammed with a bluegrass band from Placeville called MerryGold. Lead vocalist and guitarist Jillian Secor has an awesome voice, she sounds like she should be a famous singer from Nashville. I asked them why bands from Northern California sound so much tighter than bands from the Bay Area, and the banjo player said it's because they don't have cable TV up there.