Besides wineries you could visit COPIA, ride a hot air balloon, or dine aboard the Napa Wine Train.
If you enjoy art, HESS COLLECTION, has a modern art museum that is worth visiting and they do not charge for admission.
The restaurants recommend by previous poster are all good choices. Auberge du Soleil is the best place to dine with a view of the Valley. Make reservation in advance for a table on the outdoor deck.
For more info on wineries and restaurants visit
http://www.cheers2wine.com/Napa-Valley-Wine-Tour.html. You will find contact info on all of the wineries as well as direct links to each winery's website. Have fun!