I recently purchased a USB CueCat from eBay to play around with UPC barcodes, which I found out about from comments posted in a Scott Hanselman blog entry. It's fun to run around the house scanning in UPCs from household items, although the low-powered LED reader in the CueCat definitely pales in comparison to the industrial laser readers you'll find at your local supermarket. Still, you can't beat it for $15, and the PS2 version can be had for even less. If you're wondering why exactly you would want to do this, check out Delicious Library (review). Like so many things Apple, it's self-consciously cute where it should be practical, but the concept is sound.
This is a companion discussion topic for the original blog entry at: http://www.codinghorror.com/blog/2005/04/barcodes-and-qr-codes.html