Undoubtedly, John Snow´s map it is one of the most mentioned cases in Visualization courses around the globe. The 1854 cholera outbreak that killed over 700 people in victorian London, has been remembered since then as a great example of visualization for making decisions. What not so many people knows it is that this map didn´t stop any deaths, because it was just to late to do anything (cholera kills in 24-48 hours), but it served to prove that cholera way of transmission was water and not air.
You can find on the web a lot of related resources to recreate his map using software and computers. Not as romantic as the original one but it is really interesting to play with the data. Here you can download some datasets.
Vizzuality team has another interesting version made with CartoDB.