I walked past Dosa today, which is in final stages for opening next Tuesday the 29th. The menu consists largely of many kinds dosas and uttapam. Most, though not all, are vegetarian. I take it as a good sign that they're not trying to cover all the regions of India in one restaurant and are instead focused on a few South Indian dishes.
It is on the northeast corner of 21st & Valencia, on Valencia next to the health-food store on the corner.
At last -- dosas in San Francisco!