Irvine was just voted 6 best place to live: http://money.cnn.com/magazines/moneymag/best-places/
. But it's pretty blah... very suburbia.
Huntington Beach is pretty great. The city of Orange has an old town main street that's nice.
Dana Point is further south and really great. If you continue towards San Diego... my favorite fish taco stand is in Carlsbad (Cessy's). Solano Beach is a neat town also... lots of antiques and furniture stores.
Manhattan Beach is great. I'd skip Long Beach. Or what you could do is drive PCH from Huntington over the bridge over Long Beach port to San Pedro around Palos Verdes (by Trump golf course)... great views of Santa Monica and Catalina... than continue up through Redondo/Hermosa/Manhattan.
Depends a little on what you want to do. Are you going up to LA? Anything particular to eat?