Obviously if you're coming over to NZ you're probably wanting to see some nice scenery etc? If so you can't miss Fiordland national park in the South Island, there are heaps of tours every day. With that you'll get access to Queenstown, which is a bloody madhouse but has endless things to do if you're a bit of a thrillseeker. The West coast is beautiful, check out some of the glaciers along that way. Heaps and HEAPS of walking tracks to do, some take a week+, some a few days, some 30min. I'd suggest the week long tracks, they really do kick ass and it's soooooooo peaceful, just depends how much time you have up ur sleeve. Take the LOTR tour aswell if ur interested!
The North Island doesn't have as much lush scenery but has a few points of interest, rotarua's thermal activity is interesting, and theirs some good fishing in the Bay of Plenty...i'm not all that familiar with all the sights on the North Island. Check out Stewart Island aswell.
Hmmm yeah heaps of things to see and do but i'd be here all day if I was to write them all.
