Verizon are pouring $1 Billion into a nation-wide wireless network this year. They had a very sucessful trial in Washington D.C and California and hope to get the whole lot up and running over the next two years.
http://msnbc.msn.com/id/3909617/
Some McDonalds are giving away wireless access too. Check around and see who's doing what.
Apart from that, you can keep an eye out for Warchalk marked networks:
http://www.warchalking.org/