I ran across a very helpful website yesterday: www.catchwine.com. It is, among other things, a state by state directory of wineries with navigation points on a Google Map.
The mission of the site is to help you discover American wineries and vineyards and share your winery experiences by using the wine journal (available to registered users). I registered--it's free--and will update as I use the site. I expect I'll use the directory as we travel.