I once saw a man propose to his girlfriend by taking her to a specialist cake company. He'd arranged with the owners of the store to make a giant and fantastic cake, which was really a sculpture, and have it displayed in the front window.
The sculpture was of a cherub holding a wide-open book (also made of cake), and written in the book was the words, "[The woman's name], Will you marry me?"
He brought her to the window, and when she noticed, all these men in suits came out from the other stores around the street holding flowers and petals, and there was even a guy with a violin.
A bit too public for me I suppose, but it was a very creative idea in my opinion! (She said yes too)