Marokopa Falls is definitely one of the most impressive waterfalls in New Zealand. The 35 meter fall is a must see if you're on the North Island.
Marokopa Falls is located right off Te Anga Rd in Waitomo. Most people visit Waitomo for the world famous Glow Worm Caves, but I encourage continuing on down the road to visit the falls.
The tramp to the falls is very easy and should only take about ten minutes through the covered green forest. You then pop out on a wooden deck overlooking the massive waterfall. Though it isn't the nearly the highest falls in New Zealand, the classic wide rectangular shape definitely makes it one of the most picturesque.
There is a small trail that leads down to the river where you can scramble along the rocks to get a closer look at the falls. Be careful though because it's very moist and slippery getting down but definitely worthwhile if you're up for it! Enjoy!