I just noticed two newer documented chart types.
They can be used to generate Google-o-meters and QR codes.
code.google.com/apis/chart/typ ...

You can use "cht=gom" to generate a "Google-o-meter", which generates a gauge with a needle pointer.

example: chart.apis.google.com/chart?ch ...

chart.apis.google.com/chart?
chs=225x125&cht=gom&chd=t:80&chl=80%+Google

You can use "cht=qr" to generate a QR matrix code (i.e. "quick response" 2-D "bar" code).
This can encode up to 4296 characters.
A decoder application that can be used with a camera phone is also available. If the encoded text is a url, it may be treated as a link by the decoder.

QR codes: denso-wave.com/qrcode/aboutqr- ...
decoder: code.google.com/p/zxing/

blogoscoped related:
blogoscoped.com/forum/73431.ht ...
blogoscoped.com/forum/137633.h ...