ZXing - Barcode Scanner for Android
SecScanQR - The QR-Code Scanner/Generator that cares about your privacy
QuickMark - QuickMark makes everything possible.
QR Droid - QR Droid Zapper
Binary Eye - Binary Eye is a Free Open Source barcode reader/scanner and generator.
NeoReader - The NeoReader is a universal barcode scanning app that transforms your mobile phone into a barcode scanner, allowing access to mobile web content by scanning codes from virtually any medium