Instabridge - Crowdsourced free wifi (now on Android)
Wifi Locations - A community driven map for free or not free wifi locations.
OpenSignal - Mobile analytics and insights on wireless connectivity from Opensignal, the independent global standard for understanding the true state of the world's mobile network.
WifiMapper - Find free WiFi anywhere in the world
wigle.net - WiGLE (Wireless Geographic Logging Engine)