The other day I was looking for a way to generate QR codes that link directly to the Android Market. I wanted to post the QR codes so that a reader could use the Barcode Scanner app to scan the code and immediately be taken to the Android Market to download the app if they chose to do so.
After searching around for a little while (it took more time than I had anticipated) I found App Referrer. This app when installed on your Android phone will generate QR Codes as PNG files for any app that you currently have installed on your phone. These files can then be shared using the Share menu item within the application.