Triplett WiFi Hound 2.4 GHz and 5 GHz Wireless Network/RF Spectrum Analyzer to Visualize and Troubleshoot Wi-Fi Issues for Smart Homes, Businesses, and More (WFHOUND): Amazon.com: Industrial & Scientific
Inexpensive RF Spectrum Analyzers for Wireless Mics!
RF Viewer — Low-Cost, Wireless USB Dongle, RF Spectrum Analyzer
SPA-6G Spectrum Analyzer and RF Explorer Available for 3G, 6G and WSUB1G Bands Handheld Frequency Analyzing for Ham Radio, Wireless Devices, WiFi Networks, Audio Engineers (Up to 6.1GHz) Gadgets - Newegg.com
7 Best Wi-Fi Analyzers and Wireless Scanners - DNSstuff