A couple of years ago, when you thought about online interactive maps, what came to your mind? Lots of yellow. Online maps are looking a lot different these days though, and Stamen Design has played a big role in making that happen. In their most recently released project, they offer three tile sets to use with OpenStreetMap data, and they look really good.
All three are something to see, but the watercolor tiles will knock your socks off. They're computer-generated, but they look hand-drawn by a skilled artist slash cartographer (which is really what the Stamen folks are).