It's amazing it took so long for somebody to do this. FON is a Spanish company that is organizing a world-wide list of Wi-Fi access points. Anyone (including me!) who has a wireless router can join. If you agree to host the FON software on your access point, you get rights to every other FON user's access point.
So simply by making my home wireless free to my neighborhood in Mercer Island, I can access any other FON site in the world for free too.