Mt Eden -- the highest point in the city that was once a fortified Maori village (or Pa). There are several other similar hills that you probably would want to check out -- One Tree Hill (also a large park), perhaps Mt Wellington. These hills will give you views of the city, and are interesting as historic Maori sites and as volcanic cones.
The Auckland War Memorial would be good place to visit. MJ Savage Memorial Park looks good on Google Earth, but I have not been there. Google Maps/Earth is a nice tool for checking out possibilities.