An useful entry point is wikipedia.
Google search is another.
The license owner is Denso Wave.
The QRME web site is useful as well.
QRcode scannersMy selection for iphone includes i-nigma, lynkee, itagcode, flipflop, mobiletag, tagem...
Online QR code creation sitesOnline qr code creation is possible when no confidential information is shared.
QreasyQReasy creates simple url codes.
Goqr.meGoqr.me offers more possibilities, and produces images without borders
QR Barcode GeneratorQR Barcode Generator is the most complete. It offers to generate codes or uris, text, sms, mail, telephone numbers, places. It is not clear however whether using embedded images is possible (the site only offers to download the code). QR Barcode generator also offers to create 1D barcodes.
KaywaKaywa offers to create various qrcode tags (sms etc.)
Some QR code creation apis
Standard QR code formatsTo use the above php api and generate qr codes known as sms links or else, one should use the formats described on this page:
The idea is simple. When the coded text begins with http://, it is an url. If it begins with mailto: it is a mail. This principle is generalized. For instance, smsto: allows for sending an sms. In some environments, like google android, specifi tags allow for direct system integration. Synchronization for instance as on the docomo web site.