There are a pantload of mid-priced, wonderful places in the greater L.A. area.
Brunch, lunch or dinner? Asian, Euro, American, Hispanic? What are some of her favorite foods, neighborhoods and restaurants? Anything she won't eat or hates?
Don't be afraid to go to one of your favorite hangs. If they know and like you, it's quite likely they'll go out of their way to make things special for the two of you.
You can make someplace otherwise strip mall humble very special with a bottle of Perrier Jouet and the flower-painted glasses.

Plus, she'll get to keep the glasses. What can I tell you? Chicks dig flower painted glasses. They're funny that way.
Some very special places discount on coupons or other bases -- although I'm not saying I know who does what. Once you've narrowed this down to a few choices, call ahead and take care of your discount negotiations some place other than under her nose.
For instance, I've arranged substantial discounts on what would otherwise have been fantastically pricey omikase sashimi dinners in K-Town by negotiating in advance, telling the restaurant how much I was willing to pay, and accepting some limitations. Most places actually want to work with you -- especially for something like this.
Wherever you eventually decide to go, call ahead and make arrangements which go beyond mere reservations. The whole point of a dinner like this is to show her how much you value her. Take care her by taking care of all the details in advance. And by the way, that certainly includes for example telling the restaurant that you've got a special bottle of champagne for the occasion, along with its own glasses and gift box, and getting it to the restaurant so they can take care of it seamlessly.
Show your love by being considerate. That can include splurging where it counts, but not spending more than you can afford on a place which has a parking lot filled with Porsches serving food you won't really remember anyway. Besides, it will make you feel more like a mensch.
Let me know what you're thinking.
BDL
Edited by boar_d_laze - 8/13/10 at 11:49am