RConversation is behind an interesting project, FON, to create "lily pads", to use Negroponte's term, of WiFi connectivity. This deserves more words than I am devoting here, but Rebecca and others here delved deeply into the subject already and as of now, I'll rely on their words. Read Ethan Zuckerman's description of FON here. The project team is very serious about what they are doing and pragmatic about implementation.
Use this GoogleMaps mash-up to find FON accessible areas. Big names that have signed up to back FON: Google, Skype, Sequoia Capital, and Index Ventures.