Hey AZNEWGUY:
I'm a transplant from Phoenix and have lived here 20 years. My favorite way to see San Diego is by bike. Every weekend, I go for a 20 - 40 mile bike ride, usually along Pacific Coast Highway. This past weekend I did the RIDE 4 AIDS that took us through Cabrillo Monument, Shelter Island, and Harbor Island. The weather has been mild the past 2 days - a nice change from last week's heat wave.
The boardwalk that runs through Mission Beach and Pacific Beach has always been fun. You can walk, rollerblade, run, or bike and check out the local talent. There are places that rent skates and bikes. The ocean temp has been in the 70s, which is warm for here and won't last much longer. Plan on spending some time at the beach and in the ocean. You can rent boogie boards and surfboards if you're into it. You can rent kayaks either at La Jolla Cove or at Mission Bay. There are jet ski rentals if you've got that kind of money.
For sightseeing, the historic lighthouse at Cabrillo National Monument is worth the few dollar to enter the park. You can see into Mexico and get a panoramic view of San Diego. Another good view point is the cross at Soledad Mountain (free).
For dinner, 2 of my favorite places are Cafe Athena on Garnet Avenue in Pacific Beach and Alfonso's Mexican Restaurant on Prospect Street in La Jolla.
If you want any more info, PM me. Have a great trip!