Destination Wedding seems to be a big project. At the very beginning, couples may consider the following points so as to determine the direction:-
1) Blessing Wedding or Legal Wedding
If you only would like to enjoy a romantic moment without worrying about legal stuff, you could have wedding anywhere around the World. But if you would like to have a legalized wedding, some countries could not be your choice. For example, Korea does not accept foreigners' legalized wedding. Legalized wedding in Thailand will also be complicated. Deciding "Blessing" or "Legal" may help you to screen out many countries.
2) Beach Wedding, Chapel Wedding or Garden Wedding
Some places are famous for Chapel Wedding while some places are suitable for Beach/Garden Wedding. There are many stunning chapels Bali, Hawaii or Japan, which were built for weddings. Fabulous Beaches in Phuket shall be very suitable for Beach Wedding. National Parks/Gardens in Australia, Sydney are popular for Garden Weddings.
Below is a link introducing some romantic places for overseas wedding:
http://www.youroverseaswedding.com/overseas-wedding-locations.htm