I'd spend the time starting in Marlborough (Blenheim and across to Nelson) then go down the West Coast (stop at the pancake rocks and Franz Josef / Fox glaciers) and then across to Central Otago (Wanaka and Queenstown).

If in your itinerary you've got a few extra days then I quite like the Otago Peninsula. As previously mentioned you can see Albatross, Seals and Yellow-Eyed Penguins. The maximum you'd need is a couple of days though - can do the Peninsula in a day and the main highlight in Dunedin is the worlds steepest street