NetSpot - NetSpot is a free app for wireless site surveys, Wi-Fi analysis, and troubleshooting
OpenWiFiSpots - Hotspot location app
inSSIDer - inSSIDer Essential makes it easy to maintain small business WiFi.
Wi-Fi Space - Hotspot location app
Kismet - Kismet is an 802.11 layer2 wireless network detector, sniffer, and intrusion detection system.
pttrns - iPhone and iPad user interface patterns