If you are after hotels you will find a Millenium and a Hertiage in the centre - i.e. at the arts centre.
There is a holiday Inn (formerly Parkroyal) which is also very nice and the Chateau on the Park which is excellent but on the other side of the park - nice locaion but difficult to get back to across the park at night, i.e. Taxi as I would not recommend walking.
If you are after something cheaper, on Papanui Road just north main area - but easy walking has lots and lots of motels at around NZD$60 per night or less.
Otherwise there are lots of great and cheap backpackers and bread and breakfast places.
Mark
Mark