There are several currency exchange offices in San Francisco, including a couple of banks. For ordinary tourists not exchanging thousands of dollars, the ones I usually recommend to visitors in downtown San Francisco are : American Express Travel Agency (a branch on Market Street), and Thomas Cook Currency Services (on Geary Street). You can find both in the phone books. For other businesses, check out the Yellow Pages under "Foreign Exchange Brokers", or a similar name. I remember there are several around Union Square in downtown San Francisco. You can ask a concierge at any of the big hotels, and they can give you some other suggestions nearby where you are staying.