This proposal is for: The Romantic Girl. She loves fairytale endings and Cinderella stories.
Set the stage: A surprise trip to New York City
The place: A tiny hole-in-the wall NYC restaurant, sparsely lit with a few flickering candles and packed with people. You come in from the cold weather and find the perfect table in the far back.
The Proposal: Unbeknownst to your girlfriend, all of your fellow diners are your hired accomplices. As the waiter clears your main course, you give him the signal. Softly, the entire restaurant beings to sing her favorite song. At first - she doesn't notice - but as the music grows, she turns around. She looks back to find you down on one knee. As she nods "Yes!" the diners complete their serenade and toast to the newly-engaged couple!