If you have an Android device with a camera, you can install the ZXing Barcode scanner  which supports the following method. It is my understanding, however, that other barcode scanners do not support this, so as cool as this is, it may only serve a very limited audience. The ZXing app doesn't even support this method on iOS, as far as I know.
The ZXing team has a proposal for scanning barcodes to access wireless access points using a MECARD-like structure . The structure of the format is like this:
The parameter "T" can be one of "nopass", "WEP" or "WPA" for the security type. The parameter "S" is your wireless access point's SSID (make sure you append "_nomap" to prevent Google from tracking you ). The parameter "P" is the password, if any, of accessing the access point. So, a QR Code containing this information could be something like:
Hopefully other barcode scanners pick up on the proposed standard, and make this more ubiquitous. The obvious advantage is not having to type in lengthy passwords on a small screen. At any event, hope this is useful for some.