I love the style and yet how customisable it is. I've sent this to a friend of mine who's colour blind, one of his favourite hobbies has been ranting about how goolge/bing/here maps don't take into account his disability (in fairness, his is pretty rare).
http://maps.stamen.com shows the same kind of map transformations and is also based on OpenStreetMap. The Watercolor style is especially gorgeous in my opinion.
http://mapbox.com
And the tour:
http://mapbox.com/tour/