Jet away for an exotic extended weekend (the Caribbean, Tahiti, etc). You'll get away from the craziness of every day life and have time to focus on each other in an intimate, exotic, and romantic setting. There are so many options for romantic proposals here, such as a romantic dinner on the beach, a walk on the beach under the stars, and so on. You'll have to go back for your honeymoon to the scene where it all started.
Spend the weekend at a romantic Bed & Breakfast and pop the question with breakfast in bed.
Stay in a cabin in the mountains and propose as you hike to a waterfall with a picnic lunch. Find 30,000 hikes and unlimited trail maps at trails.com.
Take a camping trip and propose under the stars while you're cuddled up together by a campfire.
Head to an exotic island and get a beach front room. Have the hotel room decorated with rose petals and candles, with rose petals and candles on the beach in front of your room as well. Leave cards with romantic poems written in them along the beach walk as well. In the last card, write 'Will you marry me?'. As she reads it, get down on one knee and present her with the ring.
Take a romantic trip to Hawaii and while there, have her 'lei-ed'. Have the ring attached to the lei and when you put it on her, get down on one knee.
Plan a weekend trip, but propose before you even get there! Ask for the flight attendant's help when you board the plane and see if the pilot will announce your proposal during the flight.