One of the pacing polar bears at San Diego Zoo 5/5/01
for more polar bear in action see my travelogue
San Diego Wild Animal Park is my favorite place in San Diego (greater S.D.,it's in Escondido actually), San Diego Zoo is close second, Balboa Park is 3rd. But since S.D. Zoo is located in Balboa Park, so if you are going to the S.D. Zoo take a look of the Balboa Park,or vice versa.
Sea World is a nice place to go if you have young children or enjoy a packed theme park. There are nice beaches, Coronado island and old town for you to explore, and the weather is nice any time of the year.