Out of LA, #1 is Catalina Island. And #2, and #3 as well. But you might need a 'Catalina checkout' - ask the FBO.
On the way up to Portland recently I went to Salinas for Monterey (much cheaper than Monterey Peninsular and free courtesy car). Also North Bend (Coos Bay) Oregon, very friendly, spectacular coast. I'd also suggest Olympia for fabulous scenery on the way to Seattle. But there's no limit to the superb places you can go out there - why not route in one direction via Cody, Wyoming and visit Yellowstone?