Well I would think about Boulevard or a private room at Fleur de Lis.Both of which should be able to host a lovely dinner and have settings that can be quite memorable.
Le Petite Robert is a good suggestion also-didn't it used to be in a different location?
There used to be a fabulous place on Nob hill"le Club"or something like that?
The big places mentioned above by rjque are also a good idea simply because they are more likely to have a small private dining room for a dinner like this.