You can also feed it a floorplan and get a heatmap.
Homedale This free wireless network stumbler has some great visualization features, including a signal strength graph and a footprint mapper.This is a reliable and useful identifier of wireless signals that decodes their characteristics. WiFiInfoView by Nirsoft A free Wifi analyzer that is available in a long list of languages.
Acrylic WiFi A Wifi identifier that creates a signal quality graph for the wireless broadcasters that it encounters, showing the signal strength of each service.InSSIder by MetaGeek This Wifi visualizer is available in free and paid versions with the paid plan offering more analytical features.