Disneyland is awesome this time of year because it's pretty darned quiet the weeks between Thanksgiving and Christmas. I agree about Griffith Observatory - it's a geek paradise.
Also, there's a GREAT art museum called the Getty outside of Santa Monica which is beautiful, incredible and FREE!.
In & Out is amazing, but try to get to El Pollo Loco as well. It's darned tasty, and (like In & Out) you can't find it many other places.