ZXing's Barcode Scanner Android app (the most popular barcode app for Android; it's available on the Market) can now configure a wifi network based on information encoded in a QR code.
So you can say goodbye to having guests/patrons/visitors ask you how to log in to your wifi network every time someone new visits. Instead of having to select the correct network and type in the password (I thought computers were supposed to relieve us of this kind of drudgery), all they have to do is scan a barcode, and boom, they're online.
ZXing's QR Code Generator will help you make such a barcode (select "Wifi network" in the dropdown), after which you can just print it out and leave it in the living room.
If you wish, you can also create such a barcode yourself just by encoding the SSID and password in the barcode payload. Here are a couple of examples that illustrate the encoding method: