You can easily render 2D bar codes, known as QR Codes, with the Google Chart API, along with pie charts and bar graphs. If you haven't seen a QR Code before, you are looking at one on the right hand side (To see more, do an image search for "QR Code".)

QR Codes are a popular type of two-dimensional barcode. You can encode URLs, contact information, etc. into a black-and-white image like the one on the right. A QR-Code-enabled device can later scan the image and read back the original text. Learn more about QR Codes from Google Print Ads. If you don't have a reader Google also offers a QR Code decoder library: Zebra Crossing (ZXing).

This is how you can creating these with the Google Chart API:

Simply, there is a new chart type, qr, with attributes to tell the service what to produce:
cht=qr
chl=<text>
choe=<output>
<text> is text for the QR code. This must be url-encoded in UTF8. Note the space between hello and world is written as %20 in the following example.
<output> optionally specifies how the text is encoded into bytes in the QR Code. If this is not specified the default of UTF-8 is used. Available options are: Shift_JIS, UTF-8, or ISO-8859-1.

For the details, please read the full documentation.