While SF maintains some status in the world of critically acclaimed art - most notably with the de Young, MOMA, Asian Art and Legion of Honor museums - some of the most exciting art is available publicly either as unsanctioned street art or in public installations.
Jeremy Novy and his iconic koi and Bandersnatch with her distinctive style are two of the most prolific and recognizable local stencil artists. The famously mysterious Brit, Banksy, has several works around town (eg, on the outside of Public Works and near Columbus and Broadway in North Beach).
Amongst publicly approved art, the Mission Murals and the Black Rock Arts Foundation (with the Burning Man organization) provide some amazing works around SF.