Hotels: anywhere convenient to what you want to do!
Beverly Hills: Rodeo Drive for fancy shopping areas and chance to run into celebrities.
Beaches: Huntington Beach (hot surfers & blondes, very "OC"), Venice Beach Boardwalk (freaks and street performers), Santa Monica (nice view and pier, have dinner in beautiful upscale West LA right after)
Theme Parks: Disneyland, Universal Studios (you can also hang out at Citywalk at night), I would ignore Six Flags & Knotts Berry Farm
Downtown LA: Walt Disney Theatre, nice areas to walk around, cheap eats, very urban areas with things to do & see
Parks: www.trails.com So many beautiful parks and hikes!
If you're up north: Golden Gate Bridge, all of San Francisco's fun areas.
If you're down south: Sea World and beautiful San Diego beaches.