Post about Streeteasy switching from Google Maps
https://plus.google.com/118383351194421484817/posts/foj5A1fURGt
One of the biggest tools mentioned is TileMill, put out by MapBox
And Open Street Maps
It looks like Foursqaure very recently made a similar move, also using TileMill/MapBox tools
And the times just had an article on this
http://www.nytimes.com/2012/03/20/technology/many-sites-chart-a-new-course-as-google-expands-fees.htm