What are the codes that look like a grid of hexagons or squares? What are 2-D barcodes?

These codes are called 2-dimensional barcodes, matrix codes, or stacked codes. There are a number of these codes that are gaining in popularity. They are Code 49, 16K, Code One, PDF417, Maxicode, Vericode, and Datacode. The best bet for widespread adoption is PDF417 for “paper databases”, Maxicode for shipping information, and Datacode for micromarking applications like integrated circuits. Take a look at the BarCode-1 2-D Page.