inSSIDer - inSSIDer Essential makes it easy to maintain small business WiFi.
Waflee - Provides an effortless way to connect to your Wi-Fi
NetSpot - NetSpot is a free app for wireless site surveys, Wi-Fi analysis, and troubleshooting
Wi-Fi Widget - See, test, and share your wifi without unlocking your iPhone
Vistumbler - Vistumbler is a wireless network scanner for Windows Vista and Windows 7. Features:
WiFi Signal - Monitor and troubleshoot your Wi-Fi connection