San Francisco Opera's summer Merola program presents its second opera, Mozart's La Finta Giardiniera, 2 (evening) and 4 (matinee) August at the Cowell Theater at Fort Mason. The Merola Grand Finale concert takes place 18 August at 7:30 in the War Memorial Opera House. Tickets and more information here.
Lorenzo Pisoni returns to ACT on 3 August for a two-week engagement of Humor Abuse, his autobiographical one-man show about growing up in the circus. I liked it quite a lot when I saw it last January and recommend it strongly.
The Lamplighters present The Mikado; check here for dates and venues, because they're all over.
West Edge Opera presents a double-bill of the Brecht/Weill Mahagonny Songspiel and the Daron Hagen/Paul Muldoon Vera of Las Vegas at the El Cerrito Performing Arts Theater (just a short walk from the El Cerrito BART station); matinees 29 July and 5 August and an evening performance on 3 August.
Shotgun Players present Madeleine George's Precious Little, starting 18 August and running through 16 September.
Aurora Theater kicks off its 21st season with The Elaborate Entrance of Chad Deity, starting 24 August and running through 30 September.