Here's some more suggestions

The Coromandel Penisular - Great beaches, heaps of bush & kiyaking.

Take a trip on the Ferry between Wellington & Piction - Awesome scenery

Like Bushwalking - How about try the "Tongariro Traverse". I did it on school camp, when I turned 9. I still remember taking a break at the Emerald lakes.
And let's not forget the Milford Track - I haven't done it yet, but it's on my list of things to do.

Visit Taupo - geothermal activity, bungy jumping & other fun stuff.

Another thing which might be interesting - Black water rafting (Rafting in caves). It's something I've wanted to try my hand at.