Tourism in New Zealand is a funny, double-sided thing (and by the way, if you just want the practical tip, just skip to the next section past the three stars).
On one hand, it's an industry par excellence, generating close to 10% of the country's GDP, and the marketing skills applied to creating the New Zealand brand are truly awesome.
There are countless operators on the ground, companies which not only provide accommodation, food and transport to the visitors, but also sell EXPERIENCE: this is added value tourist industry at its most developed and subtle; New Zealand is not full of crass resorts or theme parks, but around every corner there is a company waiting to take you for an adventure. From bungee jumping (Kiwis invented that, surely the most expensive thrill on earth at close to 100 GBP for what is less than ten seconds of a jump) to heli-snowboarding to guided helicopter-transported glacier walking to private long-distance walks with hot showers, king sized beds and all meals cooked for you; Kiwis know how to package and sell their country.
Tours are everywhere, and it takes some research and some cunning to avoid them.
But, and this is the other aspect of the tourism-in-New-Zealand , it's also a country open to free (or almost free) exploration. The basic travel infrastructure, from motels to car hire, is affordable and easy to access. People are friendly, helpful and knowledgeable about their areas. Kiwis are proud of their country, they travel a lot themselves and will do their best to tell you what and where and how to see.
And the official, government bodies, who on one hand encourage the commercial operators and organised tourism, are also excellent at maintaining facilities in many a scenic area and national park, and providing great quality information that is otherwise hard to find.
i-site (official tourist information offices) often concentrate on booking tours and acting as agents for the commercial operators, but they also always have (either free or for sale for token amounts) the Department of Conservation booklet guides to interesting and scenic areas. These usually cost 2 NZD or less and often cover a particular route, area or national park, and, crucially and most importantly, they point out, grade and describe free to enter and access nature spots, walks and lookouts (which are often missed by commercial leaflets or brochures and too detailed to be covered by major travel guides).
We have used booklets on Fiordland National Park Day Walks and on Southern Scenic Route and they were both excellent, to the degree that we didn't really use our main guide book at all while touring those areas.