For the Los angeles zoo make sure you get to the zoo at the time it opens because it gets crowded later on. Also make sure to see all the new babies that have been born in the past year like the Bighorn Sheep, Babirusa, Peninsular Pronghorns (at the nursery), Markhors, crested capuchin, and mountain tapir. Then there is the older babies like the sumatran tiger cubs, borneo orangutan, and gorilla.
Also don't forget to see the new Campo Gorilla Reserve, which opened in Nov. 2007.