Tamarindo Antojeria is a cue of downtown Oakland's slow but steady revitalization. It's located in historic Old Oakland and adds a welcome diversity to an area that consists mostly of sandwich delis and Chinese food (though it is good Chinese food). I love Tamarindo's sopecitos (corn cakes topped with various ingredients), empanaditas, and tamales.
The place is very popular for lunch. For a more relaxed experience, go for dinner.