J.L.
The co-op at the Unitarian Church in Hillcrest is supposed to be wonderful. My daughter goes to The Children's School in La Jolla which is toddlers-8th grade and love the school (progressive education.) Both encourage high parental involvement, which is, of course a large commitment. If you had specifics of what you are looking for, I could give you more details about pre-schools in the area: play focused? religious? high/low parental involvement? etc...
Jen