Take a look at http://www.routeguides.co.nz
It's a great resource for planning your next tramp in NZ - both North and South Islands.
Being map orientated, you can zoom in to the region you want and browse the route segments and trips that others have uploaded.
You can put segments together and download the whole tramp as a gpx for your GPS or just browse and see what's possible.
The website is relatively new so, if you've done some tramps, join up and load your tracks for others to access.
BTW, I'm not associated with the website, other than having contributed a few trips.