Sketchy Maps with Geometry Smoothing
mapbox.com
mapbox.com
Here's Stamen's watercolor map: http://maps.stamen.com/watercolor/#12/37.7706/-122.3782
http://infosthetics.com/archives/2010/06/bing_destination_ma...
Love the end result of the bezier curves shown on the map of the Caribbean, but really thought the napkin sketch feature was fantastic for directions.
For example a GPS device will give sometimes give you a ridiculous number of turn by turn directions in a row. Go 100 feet merge right, go 200 feet merge left, go 50 feet and take a right, go 300 feet and make a left.
Obviously not nearly as involved as this, but a nice example of what a really simple transform can do aesthetically: It just median-filters Google Maps, which has the effect of removing text, simplifying boundaries, and producing large flat color areas.
There's already a nice collection of other twists on the slippy-map-as-art thing here. One more is Stamen's Pretty Maps, which does the heavy lifting in SVG and combines Flickr shapefiles in very interesting way: http://prettymaps.stamen.com/