Shopping in San Diego [1] runs primarily to malls and shopping centers that offer a good, if selective, experience.
Downtown [2], wander the Gaslamp Quarter [3] for San Diego-grown clothing or hit the immense Horton Plaza [4] for stores you know.
Old Town [5] is fun for unique, Mexican souvenirs and is a short jump from Mission Valley where the mall is king.
Farther north, La Jolla [6] provides a more relaxed, upscale experience.
Links:
[1] http://www.moon.com/destinations/california/san-diego
[2] http://www.moon.com/destinations/california/san-diego/shopping/downtown
[3] http://www.moon.com/destinations/california/san-diego/shopping/downtown/gaslamp-quarter
[4] http://www.moon.com/destinations/california/san-diego/shopping/downtown/horton-plaza
[5] http://www.moon.com/destinations/california/san-diego/shopping/old-town
[6] http://www.moon.com/destinations/california/san-diego/shopping/la-jolla