Some Very good climbs are on the long loop of the old Como St ride in Tustin. The last time I did this ride was about 9 years ago and it left the tustin marketplace around 8:30 on a Sunday.
If you want the route PM me and I will map my ride this for you.
Another great hill climb is in Laguna Beach from the beach to the Top of the World. It is not that long and not that high but has some good 12-14% pitches in there.
If you like out and back the Trabuco canyon is a great ride although the pavement was not the greatest the last time it did the ride many years ago. You can add this to the Como st ride and get one hell of a workout.