I was in SoCal three years ago this summer, and I spent 4 days in San Diego (Coronado to be exact). First off, book a hotel room very soon, since there is a big comic book convention in San Diego in late July, and all the hotel rooms are booked solid. My family was lucky to get a room, since someone cancelled at the inn we stayed at (it's a very nice place with affordable pricing, I can find the name if you want Duke).
But there is tons to do in San Diego. First off, take a harbor tour. I know Duke will not be dissapointed since first of all, you get to see many warships of the US Navy and US Marines. Often, there are Navy aircraft carriers docked there, but I missed one by a few days unfortunately. Also on the harbour tour, you get to see the Naval Air Station on Coronado. This is a scrapyard for old navy fighters, as I saw tons of F-4s, F-14s, and F/A-18s awaiting disposal. There was also a C-17 there when I took the tour! If you are looking for more aircraft, there is an aerospace museum not too far from the zoo which has many beautiful planes and replica planes, including a magnificent F-4 Phantom.
Some of the other main attractions in San Diego like Sea World and the Zoo are great places to visit for the day. I went to both places and got very good days out of them. Also make sure to visit old town. Lots of history there and there are some incredible Mexican restaurants there.
If you can, take the three hour drive up the interstate to Los Angeles. I was there for a few days for a wedding, and it's a good place to go to for a few days. Lots of shopping in the outdoor mall in Santa Monica, and lots of good restraunts there too. And of course there's Hollywood and Beverley Hills. And also since it's on the way to LA, there's always Disneyland, a must see if you have any kids. Heck, go there if you don't have any kids, it's a great place to go to. You can easily spend 2 or 3 days before you have gone through the entire park. And you MUST check out the restaurants around Disneyland. I ate at a cajun restaurant there, and I can still remember how good the pasta jambalya (sp?) was. If you don't like cajun, there are dozens of other great resteraunts there.
And as for the weather, the coastal regions are absolutely gorgeous. The temperature was perfect, and there was no rain whatsoever for the 1.5 weeks I was in SoCal. I never went more than 10-15 miles inland so I can't comment on the weather there.