National Bike Registry
I have no affiliation with the National Bike Registry, but on their website it states that they are endorsed by Kryptonite. They are also an official licensee of the National Crime Prevention Council (NCPC.) So I'd say it's worth checking out.
What is it? The National Bike Registry is the link between you and the people who can get your bike back.
For a small fee, you can register your bike, greatly increasing the chances that it will come back to you if it is found. (Note that unfortunately, this does not increase the chance that your stolen bike will be found in the first place.)
It is basically a serial number database linking you, your bike, and law enforcement.
Thousands of bikes are recovered, but very few are returned to their owners because they cannot be found. I figure the only thing worse than having your bike stolen is having your stolen bike found, but not being able to get it back.
National Bike Registry solves that problem!
The price isn't bad. Just $10 will cover your bike for 10 years. Click here to register your bike.
(If you are in the UK, there is a similar service there - BikeRegister.com.)