The Wi-Fi Alliance has its Wi-Fi Zones search up and running: You can search by many parameters for hot spots that have opted into the Wi-Fi Zones branding program. (Anyone know anything about axcess2go, which appears to suddenly have a dozen locations in Seattle?)
See also EZGoal Hotspots, Wifinder and 802.11hotspots and of course Boingo and T-Mobile Hotspot.