Paul McCartney and Tom Petty both at the Hollywood Bowl are 2 of my favorites. That venue is just spectacular. I've seen Petty around a dozen times, all of his shows are awesome, never miss him when he is in So Cal.
Rebelution and Slightly Stoopid at Irvine Meadows was a great stoner fest (if you like Rebelution and have never seen them live do it, they are phenomenal).
Pepper at the Hard Rock poolside in Las Vegas was an awesome drunk show.
Any No Doubt so cal show.
Any Offspring show, especially last summer at the OC Fair.
Iration at The Cave in Big Bear, awesome small venue.
Green Day at the Olympic right before they released American Idiot...I thought Jesus of Suburbia was like 4 different songs when they played it.
Now back into the Junior High/High School Days:
Pop Disaster tour at Irvine Meadows with Jimmy Eat World, Green Day, and Blink 182
Sugarcult/Unwritten Law at a small venue in LA, I can't remember which one.
Yellowcard and New Found Glory at Chain Reaction in Anaheim.