Oh, what a great thing to look forward to! In Southern California I think you'll most likely see Anna's. Roufous may pass through as they migrate up the Pacific coast (and ruin any sense of peace in the neighborhood, as they do here just one state over :) ), and Allen's I'm not sure about. I've read that Allen's are non-migratory in southern Cali and can move up into the western part of the state and up to about the Oregon state line. I have a couple friends who have witnessed Costa's hummingbirds in southern and western California, but their experiences have been brief. Anna's I think you should get pretty much all year, which is a great thing.

Don't forget the Black-chinned Hummingbird as a breeder in addition to the aforementioned Anna's and Costa's as potential breeders as well as Rufous and Allen's during migration. From the range maps in the Birds of North America accounts, Allen's breed further up the coast in California than San Diego, but you could get them as migrants.

BN