As OpenStreetMap has matured into a viable replacement for other proprietary sources of map data, some great, great things have been happening in the world of online maps. At foursquare we've been excited and proud to join a growing movement in using open map data on our website, with OSM-powered maps from our friends at MapBox.
Today the frontier of open source mapping has been pushed a bit further by the folks at Stamen (no rookies in the game of making beautiful maps), who released a set of three OSM-based Creative Commons-licensed map tile sets. All three are great, but Watercolor is breathtaking. I literally gasped when I loaded the page. Go take a look.