The CueCat is a PS/2-based barcode reader. Wired gave away hundreds of thousands of them free with one issue of the mag, and you could also get them free at Radio Shack. They were intended to be used to scan in barcodes next to ads in catalogs and magazines, but they were most useful when you modded them to read regular barcodes, so that you could do things like build a database of your books and CDs by scanning the UPCs on their backs. CueCat even threatened to sue the hackers who figured out how to manage this trick!
Years later, there are two million CueCats up for sale on a liquidator's site at $0.30 each in quantities of 500K or more.