You can never go wrong with hardy
lilies and a few floating plants such as
hyacinth and water lettuce. Maybe a
taro to provide a bit of shade, and an elevated platform to stand on.
What are you planning on as far as the actual pond? Size, depth, filtration, etc?
Also, I would not go entirely no fish. Throw in a few cheap mosquito fish or guppies to make sure you don't get mosquito larvae.