I have been helping out with Let’s Read LA for the two years- it is a great program where you work with under privileged Elementary school children to help them with basic reading skills. It meets on Saturday mornings from 10:00am to 12:00pm. They are in the process of putting up a page here (Los Angeles Volunteering Opportunities) where you can learn more information if you are interested.
Additional volunteering opportunities in LA through LA Works can be found here.