Quickly browse through different available Wireless networks for the iPhone?
As fas as I know, there is only a concept video for Notification Center WiFi seleciton, and there is a Simple Wifi for Notification Center Cydia tweak that will show WiFi info in there, but I don't think there is actually something that gives you exactly what you want.

But really, it's just two taps. Settings icon > WiFi section. That shows you all available networks. If your current WiFi network goes off, a list of available networks will automatically pop up.