If you're running your Raspberry Pi in headless mode, it's difficult to troubleshoot Wi-Fi problems. Raspberry Pi Spy points to Wavemon, a Linux utility that also happens to work great on the Raspberry Pi in the command line.
With Wavemon, you get a stack of statistics about your Wi-Fi network, including a graph of your signal levels, all the wireless networks near you, and a preference page where you can boost the signal. It's a little thing, but it's super-helpful for anyone troubleshooting Wi-Fi issues on their Raspberry Pi.
How to Use Wavemon to Monitor Your WiFi Connection [Raspberry Pi Spy]