It used to be you could change anything layered on top of a map, but you couldn't change the underlying map itself. Now you have several options for changing the color palette and the visibility of different objects that make up your base map. The options vary on the amount you can customize and how much work is required. But all three of these APIs can have you map scripting with style.
The limitation so far has been that users and developers usually have to wait for the big players like Google, Yahoo and Bing to add the relevant information to their maps.
CloudMade has conveniently side stepped this issue by allowing its maps to be collaboratively edited, making it a kind of “Wikipedia for maps”. The results have been quite impressive, as TechCrunch reports.