StreetTech just ran an item about a website called LibraryThing. It lets you populate an online catalog of your books by scanning the barcodes on the covers into your computer.
The interesting question is - How do you scan a barcode into a PC and onto the web? Gareth from StreetTech suggests using something called a CueCat. This is an old barcode scanner gadget that was distributed freely to magazine subscribers a few years back (all Wired subscribers received them at some point).
These things are no longer manufactured - the company went bust after it was discovered that the company kept track of what specific users had scanned violating their privacy. Buying a standard barcode scanner like the ones you see at your local supermarket is somewhat expensive (starting at ~100$). Problem.
The solution? Barcopedia! This website connects to your webcam and if you point it at a barcode, it will scan it in real time and give you the full details for the item (provided it's is in their DB of course).
I can tell you I was as excited as a little boy the first time I scanned a book, the website pinged and the details showed up on the screen.
I wonder what other magic can be done to barcodes via Barcopedia and how extensible it is. If it has a decently open API, I can imagine myself cataloging my entire library through their service.