The 2nd biggest Opera in North America (to the Met in NYC) - the season runs roughly from September until July.
Tickets range widely (starting at $10), but there are a variety of ways to save - including 200 "standing room only tickets" for each performance. Otherwise, the Opera generally performs two free shows annually - one at the Stern Grove Festival and "Opera in the Park" at Golden Gate Park - in addition to a live simulcast at AT&T Park.
For lovers of classical performance arts, the Civic Center rocks... err, overtures (?!) - the Ballet performs in the same building as the Opera, and the Symphony is across the street.
Address: 301 Van Ness Ave, SF
Website: http://sfopera.com/