Zxing-android is a project mainly written in ..., it's free.
custom build of barcode scanner for android with portrait oriented preview - patches from: http://code.google.com/p/zxing/issues/detail?id=178
Custom build of Barcode Scanner for Android which forces the preview display to use portrait mode. This build also contains some hacks to make scanning faster. The application I was developing needed a bit faster scanning, so I cut out the delay after a barcode is found. It should instantly send the data back to the Intent that requested it.
Works on NexusS4G with zxing 1.7 source as a base.