The most important thing that I can tell people is if you are choosing between renting a car or riding the trolly, rent a car ahead of time. The public transportation is awful, especially if you are not from a bigger city and don't know how to use it. Reserve a rental car ahead of time, don't use the small rental agencies (like the ones they may have in you hotel lobby). They will charge you a large deposit (without informing you they are doing it!) If you reserve one ahead of time, most larger companies don't require a deposit. Also, the taxi drivers are insane drivers and they will take you the long route to get extra money, so if you know where you're going, make sure you tell them to go the shorter route.
On a lighter note, our favorite thing to do was go to the San Diego Zoo's Wild Animal Park near Escondido.It's about 20 miles north of San Diego, but it's definetly worth the drive. We also enjoyed Seaworld and the Zoo.We also went to Tijuana on a tour bus, but we wasted a half a day doing that. I had never been to Mexico, so I wanted to go, but I didn't enjoy it at all and the shopping wasn't good like I'd heard.

Kayaking down at La Jolla Shores is a fun time! There are about 4 or 5 different companies located on Avenida de la Playa that offer kayaking. You can either go with a tour or on your own. The Shores (as we locals call it) is a mild spot that offers calm enough waters for inexperienced kayakers of all ages. If you go during summer- don't get scared of the sharks! The Shores is home to bottom feeder sharks that don't particularly like the taste of humans (good thing).

Drive along the coast until you reach the swanky area of downtown La Jolla. This is a great place to window shop, spot Ferraris, and maybe even see a celebrity (Myke saw Anna Nicole Smith last time we were there). La Jolla is the playground of San Diego's rich people...so it's always fun to just sit at the coffee shop and people-watch. So many different cars, styles of dress, small chihauhaus, and all types of plastic surgery all in once place! Make sure to go down towards the water and see the beautiful coastline this area has to offer. Check out the seals at the Children's Pool!

If you have a car, drive out east on the interstate 8. Within 10-15 minutes you have left the hussle bussle of the busy city and suburbs and are out in the beautiful nature that makes up southern California. There are many hikes out this way--my favorites being the ones off Sunrise Highway exit. Afoot & Afield in San Diego County is a GREAT book on all the hikes in the area.

Gaslamp is a fun place to go on a Saturday night. Make sure to dress to impress as lots of the clubs have dress codes. No t-shirts or flip flops (especially for all you guys out there!). Definitely bring the cash $$ as this will doubtfully be a cheap night on the town! Park in the Horton Plaza garage to save some $ --just buy a pack of gum to get your parking pass validated.

Pacific Beach, stroll down Garnet Avenue and check out all the bars, restaurants and little boutiques. Cute clothes and fun accessories for great prices at many of the stores. Make sure to stop by Fred's Mexican cantina/grill for a delicious burrito or tacos. Taco Tuesdays they have cheap deals after 9pm there! Yummy margaritas and you can get pitchers! For the adventurous, try out the WaveHouse wave simulator where you can attempt to surf a man-made barrel. This place also has 2 bars on the sand, hammocks to sit in, and music. Another idea is to take a walk out onto the pier for sunset--but make sure to have a jacket as it gets pretty chilly out there! Another great sunset spot is Lahaina's grill which is a couple blocks south of the pier on the boardwalk. Enjoy a pitcher of beer here on their huge beachfront deck.

One thing you have to do in San Diego is grab a sandwich or any other lunch item and take it to Balboa Park. It is a beautiful location with many things to do when your'e done eating. You can head to one of their many museums or grab a cocktail at The Prado- a restaurant ideally situated in the middle of the park. The entrance to the park is free so you can wonder around for hours and not worry about the money you owe on your way out.

Ok, you can find lots of stuff about san diego on the internet. My advice to you is, since San Diego is near to Mexico, go to Mexico. The city nearest to San Diego in Mexico is Tijuana (pronounces as tia-huana). Don't go to Tijuana with your car! Although going to mexico is fun, remember you are still in a foriegn country and it can be dangerous. We heard lots of sad stories about being in Tijuana. If you really want to go there by your car, get your car insured which you can do in the USA at the last border exit. You can go there by trolley. The trolley in San Diego goes to the Mexico border.
Mexico doesn't require visa from anybody going their country through San Diego. If you are american, you even don't have to bring your passport. Your state ID is enough to come back to states. When you go to mexico, there is a big, huge arc in the center of the Tijuana. THe parties are going on around it. Every thing is super cheap in Tijuana compared to San Diego. You can find a trolley anytime when you decided to come back. Just remember that, the last trolley goes back to San Diego at 1 am. I hope you enjoy it.