Although not really a hummingbird haven like southeast Arizona, southern California still hosts six species of the Trochilidae family.
The most common is the Anna's Hummingbird (Calypte anna), which can be seen even in urban gardens. As in all of the these species, the male is the one that has the more colorful gorget, especially given the proper light and angle. Male Anna's have an iridescent magenta or reddish pink crown and gorget. By the way, it's name was derived from Anna Massena, duchess of Rivoli, by Rene Lesson, an 18th century French Ornithologist and Herpetologist.
Arguably just as common as the Anna's is the Allen's Hummingbird (Selasphorus sasin) which can also be easily seen in parks. It is generally rufous in color, the male having an orange-red gorget. It's forehead and back has a green color. The name commemorates Charles Andrew Allen, a collector and taxidermist of the early 19th century.
Similar looking and often confused with the Allen's is the Rufous Hummingbird (Selasphorus rufus). The male Rufous can be best distinguished from the Allens, by having a lesser amount of green on the crown and back. Rufous Hummingbirds are also migratory and can be more commonly seen in Southern California in spring.
Another migrant, seen only during the summer months is the less colorful Black-chinned Hummingbird (Archilochus alexandri). It's dark chin becomes iridescent deep purple at the right amount and angle of light.
The following two species are less common than the previous four. It was just sheer luck that I was able to photograph both at the Eaton Canyon Park in Pasadena not far from where I used to live.
The Costa's Hummingbird (Calypte costae) is a resident of arid and semi-arid regions of California and Arizona. However, in summer, it seeks shelter from the heat and inhabits chaparral and woodlands. It is similar to Anna's in terms of the color of the male's throat. However, the Costa's gorget extends out to the sides.
The smallest bird in North America is the Calliope Hummingbird (Selasphorus calliope). It is also a migrant and can be seen in southern California during its spring and autumn passage.The male has wine-red streaks on its throat instead of the usual gorget.
Information derived from wikipedia and allaboutbirds.org