The Art in Public Places program sponsors hundreds of pieces of art in (you guessed it) public places, by local artists. But those aren't the only pieces of art around. There are murals, for example the mural on the wall of Old Soul Coffee.
Russ Andris documents hundreds of murals and other public art throughout the Sacramento area on his site: http://www.pbase.com/southyuba/public_murals_sacramento.
Local blog, Pedestrian Art, Sacramento (http://www.sacpedart.com) includes a map of public art in Downtown/ Midtown with detailed information about each piece of art, the artist, etc.