According to Wikipedia and Kaywa who created the below graphic, there are four types of 2D Barcodes: QR-Code and Datamatrix, Maxi Code & PDF 417. From my research, these are the most popular and have the furthest reach, but host the most limitations and vulnerability.

However, according to http://www.adams1.com/stack.html there are many more variations. Further research continues to find new variations everyday like the unique QR Code used by Doritos below.

Recently Gizmodo published an online article which describes the newest barcode titled The Barcode Update You Never Asked For, But Still Need. As this video describes in more detail, the code is about the size of a small dot and basically is comprised of multiple, micro-inscribed datamatrix codes that an out of focus camera can capture and read. The ability to inscribe and utilize multiple datamatrixx codes as a small dot definitely opens up more possibilities and is prettier on the eyes, but the need for a regular, out-of-focus camera will produce some limitations. Again, it seems like the possibilities are endless and the the deeper I swim the bigger the ocean seems. Even Louis Vuitton has his own designer 2D Barcode!

1. What is the Standard 2D Barcode Size?