OpenIntents

ZXing is an open-source, multi-format 1D/2D barcode image processing library implemented in Java. Our focus is on using the built-in camera on mobile phones to photograph and decode barcodes on the device, without communicating with a server.

Note also the project at http://www.onbarcode.com/products/android_barcode/

http://code.google.com/p/zxing/