A derivative of ZXing's Barcode Scanner version 4.2 with support for front-facing cameras, including support for devices like the Nexus 7.
If your device has multiple cameras, a button will appear in the top middle of the screen, which allows you to cycle between them.
Note that front-facing cameras can be lower quality and less able to scan fine-featured barcodes, but coarse QR codes scan just fine.
This version no longer has the "view finder" (highlighted rectangle in the center), which should make it easier to use with a front-facing camera. Another tip is to put the device down and hold the item to be scanned in front of the camera.
If your device does not have a camera at all, this app will not work.