Te Reinga Falls is a series of 35m waterfalls creating lots of mist that often result in rainbows. Given the volume of water that flows on the Ruakituri River, this area was once considered for hydroelectric development. I've seen old photos of the falls on the other side of the river providing very satisfying views of several of its waterfalls. However, I'm not sure if that view is accessible anymore.
For more information on this waterfall such as...
maps
directions
detailed descriptions
refer to A Guide to New Zealand Waterfalls (Story Nature Press).