@LadyCheri: The bus system in San Diego sucks. Actually, the entire public transit system sucks. Yes, there is a trolley but it doesn’t take you anywhere touristy- just out to east county and back or down by the border. Definitely rent a car- especially since you would NOT want to pay the money to have a cab take you up to Julian and back!
Also, I have to disagree with PP and say that the safari park is better than the zoo (although you’ll find this is a matter of debate!), and also not drive through! You park, you pay for your ticket, you go into the park… and they have the standard zoo-type exhibits but they also have this big wide open area with all of their african safari animals (giraffes, rhinos, etc) running free basically (predators are in separate areas) and you can pay a small fee to go around it on a tram or pay a bigger fee and they’ll take you right through the middle of it. It’s way. freakin. cool.
As far as snorkeling in La Jolla goes- you can rent your snorkeling gear from anywhere near the cove, although they don’t actually sell it on site. When you drive to the Cove (which by the way is only 5 minutes from La Jolla shores, although La Jolla shores is a great beach for laying out, boogie boarding, etc whereas the cove is much better for snorkeling), and you head down the hill (you’ll see what I mean when you get there) there’s a little dive shop on your right hand side… they should rent snorkel equipment to you for the cove.
Also, at La Jolla Shores, you can rent boogie boards on site for some beach fun and surf boards too I believe- you can even buy lessons. And the reason I recommend LJS over Coronado is that Coronado, in my opinion, is more otu of the way and has waaaaaay too much sand before you hit the beach! Very wide beach, and also no grass. LJS has grassy picnic areas, nice restroom facilities, soft sand, and nice water… plus it’s super close to the Cove for snorkeling (oh, and down the street from the Cove is the Children’s pool- walk down there to see the local colony of sea lions. There’s a sea wall you can walk out on and on one side of you, the waves are crashing and on the other side, it’s a calm cove and you can see the sea lions pretty clearly. Really cool.)
Also, FWIW, I second the yardhouse- delicious!!!! And also, try Baja Betty’s for a good night out (in the hillcrest area 5 min from downtown) or Urban Moe’s- both great places (they’re in the gay district of San Diego, but they’re both really really good and worth checking out).