Martinborough is a must. We spent some time down there and loved the area. Be sure to get a bottle of Brody Estate Pinot Noir 2007 Our personal favorite of the local wines there.
You also might look into a day trip down to Cape Palister (sp?). It takes about an hour from Martinborough to get there but has a very cool lighthouse and the seals are all over the place on the rocks near the water.
Here are some pictures we took on our blog of the area:
http://howellsinnewzealand.blogspot....pa-region.html
If you are into tramping Mt Holdsworth is right in the area and has some good views.
http://howellsinnewzealand.blogspot....rth-tramp.html