Delaware has great beaches in the southern part of the state. If you are planning for a longer trip, consider going to Dewey Beach or Rehoboth Beach. The beaches are a ~2 hour drive from the wedding location.
NYC and Washington DC are within a 3 hour drive from the wedding venue. Alternatively you could take an Amtrak train from Wilmington,DE to either location. If you do plan on taking the train, consider booking tickets several months out. Prices do go up as you get closer to the travel date.
If you would like to take advantage of tax free shopping, this is your place.
Great option for those with children
One of the bride's favorite restaurants in the area