Haven't seen any votes for the mid-Atlantic beaches. They might not be the most beautiful in the entire world but they are nice. I recommend the Delaware area (Rehobeth, Bethany Beach, area.) The Delaware beaches are not AS developed as their neighbor beaches in Maryland. Rehobeth has some very nice restaurants and shopping areas (outlet stores and boutique style stores...the whole range.) Bethany is more of a family/residential beach area. If you are looking for more to do, head down the road to Ocean City Maryland. Miles of beaches! There is a lot more activity such as the boardwalk, shopping, high rise condos/hotels, restaurants, bars.
Are you restricting yourself to the mainland? If not, I highly recommend Hamoa Beach in Hana, Maui. James Michener named Hamoa Beach the most beautiful beach in the entire South Pacific. It's a crescent shaped beach with soft white sand and in the distance you can see the Big Island. I also recommend Hapuna Beach, north of Kona on the Big Island.