Wifi Analyzer for Android helps you pick the best channel for your Wi-Fi network
Still, most routers and access points come with a pre-set default (that appears to be 11, at least for the routers around me). When you have several routers broadcasting on the same channel, this can lead to some interference and a performance hit. If you live somewhere fairly isolated and your Wi-Fi signal is the only one in range, you've got nothing to worry about.
On the other hand, if you're trying to survive in a dense urban jungle, surrounded by paper-thin walls and lots of Wi-Fi-using neighbors, you may gain a bit of a performance boost by switching your access point's channel to a less congested one.
Wifi Analyzer is an Android application that helps you figure out exactly what that channel is. The screenshot to the right shows how channels 9 and 10 are occupied by a couple of wireless network fighting over the same frequency, while my network (the red one) lives comfortably on channel 1.Wifi analyzer offers several views, including a simple "channel rating" screen with no graph, if you just want to quickly figure out what's the best channel for you. A beautiful app, and free. QR code is after the jump.