Go whale watching at Kaikoura, you really do need to book in advance though. It really is the best whale watching we have done anywhere in the world. The crew are very helpful, friendly and they certainly know how to find the whales and get good views of them. When they say click your camera because the whale is going to dive... don't think just do it. They are always spot on with the advice!
It is free of charge and you get to see the wild animals up-close.
You can see them at a number of locations but I recommend Kaikoura, South Island.
Go to Kaikoura on the South island and visit the seal colony there. As you travel south to Kaikoura the road follows the sea for some time and there is the colony you cannot miss it.