Good news for those that are upgrading to an Xbox 360 Elite, you can now order your free data transfer cable free from Microsoft. However, this isn't available to anyone but owners of the new Elite version of the console.
You also have to provide the serial numbers of both consoles on the order form, so you can't try to cheat Microsoft out of a cable either.
If you'd rather just upgrade your hard drive of your older HDMI less console, then this cable is included with the overpriced 120GB drive. However, this is a onetime use only product, so once you've use it once, it becomes defunct, thanks for that one Microsoft.
You can find the order form here, but it's only available to Xbox owners on the American continent, the rest of us are unlikely going to get the same offer. (note that this is a PDF link)