At
http://www.jiwire.com you can specify an area and it will list all the wi-fi locations it knows about. It knows about almost 40,000 sites around the USA. It also lists the provider and, in many cases, the pricing. I downloaded their free directory so can search it when I arrive at a park and am not online yet. It has an option to update the directory on my pc when I'm online. Pretty nice setup to have around.