I've got two great suggestions for you:
Maui (lush, tropical, extremely romantic, and so many great places for pampering). My husband and I took a week-long honeymoon to Maui and it couldn't have been more perfect.
In Maui I suggest the Hyatt Regency Kaanapali Beach or the Four Seasons in Kapalua. We stayed at the Hyatt, and it couldn't have been more perfect. Wonderful pools, restaurants, artwork, and amenities on a beautiful stretch of pink Hawaiian beach. There are a number of wonderful spas in the area. My in-laws stayed at the Four Seasons in Kapalua. They enjoyed it immensely, especially the spa services and the secluded locale.
Aruba (wild untamed-looking landscape, low humidity, lovely beaches and superb shopping). My husband and I celebrated our five-year anniversary in Aruba this summer with my sister and some friends. It was simply perfect! The beaches in Aruba are some of the finest I have experienced and the water is clear and calm, perfect for a midnight dip.
In Aruba, I strongly suggest the Radisson Palm Beach or the Hyatt Regency Palm Beach. Both are first-class luxury resorts with top-rate spa services, dining and casinos. The beach--Palm Beach--on which both resorts sit is gorgeous and absolutely perfect for swimming, sunning, snorkeling, etc. I adored Aruba and can't wait to go back.
Both would be perfect choices for a romantic beach honeymoon.
Good luck! And do let us know what you choose. I am always looking for the next "perfect" vacation spot!