Stay in a cabin in the mountains and propose as you hike to a waterfall with a picnic lunch. She'll be able to share it with her friends and family. Or send her an eCard that will be delivered to her at work. Rent a billboard and drive her by. Put it up with the ads before a movie and take her to see the show.
Sky write it.
Have a plane fly a banner. Put an ad in the local paper. Have it displayed on the scoreboard at a ball game. Paint your proposal on the roof then take her flying over it. Have the ring tied to one of the flowers.