While you can find winery addresses and pull them up on a map, finding specific vineyards has been a larger challenge. Maps of AVAs (American Viticultural Areas) are readily available but usually at sites focused on that region exclusively. Everyvine is an exciting tool and I would like to take you on a brief tour. Here is the link: http://www.everyvine.com/
There is a new website featuring maps of wineries, vineyards and AVAs that is free to browse and you can even embed the maps on your website, if you choose (this can cost money). You will find only domestic wines represented but Oregon and Washington are included with California. Surprisingly, and impressively, they include West Elks region of Colorado. I would love to see them include Missouri, Virginia, Indiana and Texas (among others) as well but they are off to a good start.
Being able to zoom in and out (simply scroll within the map) on a region and toggle between a map and satellite view is amazing! Here is a map of the Willamette Valley. You can get a real picture of where the wine regions sit in relation to cities (often not included in wine-centric maps) and then you can get a glimpse of the topographical situation to help understand things. All while the region remains delineated on your screen. This is the most exciting aspect of the website to my mind.
You don't need everyvine to find a winery, finding an address and pulling it up on a map is easy. However, the vineyards are not always located next to the winery itself and it can be quite a challenge to find them on a virtual map. Everyvine does it for you, again with marked boundaries. I found the vineyard search option a bit confusing but they do appear to still be in beta, so perhaps some bugs will get corrected. When you find a vineyard, you need to click the name to get to the map. Here is the famous Shea Vineyard in Willamette Valley.
They have maps for sale as well, be sure to check out the options. This website is a wine geek's dream come true(!) and I hope they are wildly successful, eventually bringing us the entire globe.