You didn't say whether you were looking for preschool for right now, or looking ahead toward kindergarten. For preschool, I'd recommend any of the several Kidsland home-based daycare/preschools (mostly located in S. Berkeley, but also w/locations in San Leandro).
If you are looking ahead toward kindergarten plus, Oakland Unified School District offers dual-immersion Spanish/English in several of its public schools, including Melrose Leadership Academy, Manzanita Seed, Community United, Global Family School, and Esperanza Elementary. I chose Esperanza for my son this year, and have been impressed thus far w/the level of caring & commitment amongst the teachers, admin, and after school staff. All of the Spanish language arts teachers are native speakers. There are some of the usual public school issues (class sizes larger than ideal in some grades, for instance), but for an Oakland public school, I'd say they make a dedicated contribution to the community. Parent who switched from private to public