Tommy's Mexican Cantina is the place. This spot is considered to be the largest importer of Tequila in the US and has a great atmosphere. The owner,Julio, behind the bar, will know you by name after the first visit.
Address: 5929 Geary Blvd. @ 24th
(415)387-4747
http://sanfrancisco.citysearch.com/profile/907656/