Watson's Way, run by Pat and Paul, is a clean, welcoming hostel in the little village of Renwick bang in the middle of Marlborough wine country.
Toast and jam is provided for breakfast, there's a nice lounge with a television. Bikes are available for hire ($10 if you're staying at the hostel) and Pat will offer tips for the best route around the wineries and which ones to visit for tastings.
On SH6/SH63. Blenheim is the nearest town.