Depends on the the girl- some like high-society, so Hollywood/beverly hills would be fun for them.
If you want to stick to the OC-
High $$$ newport ca
Mastro's Ocean Club
(949) 376-6990
http://www.mastrosrestaurants.com
Then go to Irvine Improvcity for a laugh-
3415 Michelson Dr
Irvine, CA 92614
(855) 624-6776
cheap date-
Take her to Bucca Di Beppo
then to Signal Hill park to see the view. Bring a blanket and some champagne
E Hill St and Cherry Ave
Signal Hill, CA 90755
Or go to Downtown Disney, pick a place to eat- then if youre into cheezy romantic, bring some folding chairs and make it up to the top of the parking structure in time for the fireworks show.