OS X 10.8 has a well-hidden feature that lets you visually chart wireless performance in real time, get a ton of useful information about all available wireless networks (even hidden ones), and perform a wide range of network troubleshooting within a simplified interface.
To access this useful feature, hold down the Option key while clicking on the Airport icon, select Wi-Fi Diagnostics, then press Command+n after the Wi-Fi Diagnostics window opens. This will open the Network Utilities menu.
From the Network Utilities menu, click the Performance tab to see the real time signal strength and network traffic charts. The Wi-Fi Scan tab shows details about all the networks within range, including the security types used by each. The Bonjour tab shows all devices on the network broadcasting using Bonjour, and addresses for each. The Tools tab provides a simplified interface for running a ping, traceroute, netstat, lookup, route, whois, finger, and ARP.