I recently added a feed to the photorant archive page marked "UPCOMING" — it's driven by SF Gallery Listings on Upcoming.Org
These listings can be cross-posted, subscribed via RSS, or you can set up a free membership in Upcoming and have them in your personal list, complete with (if you like) little email reminders before an interesting show etc. Or add new events if you find out about them.
Some big deals (to me) in the next few weeks: EIKOH HOSOE (!!!!) and ALEC SOTH lectures at SFAI.