You wouldn't leave the door to your house unlocked at night in the hopes that you'll catch a thief red-handed, would you? Then why wait until thieves open credit accounts in your name before being notified that there's a problem.
Up until recently I was a big proponent of Equifax's Credit Watch service, whereby an email notification is received whenever a change occurs to your credit report. You then have to sift through the changes and make sure nothing fraudulent has occurred. Sounds a little too late to me, after all if something has happened and somebody has managed to steal your identity and open credit in your name, the damage is already done and you're left a mess to clean up.
Enters LifeLock, this is a service at the forefront of a new type of credit protection that's more proactive and preventative in nature than a Credit Watch service. When you sign up with LifeLock, which costs about $10/month, the first thing they do is set a Fraud Alert at all of the credit agencies and keep the Fraud Alert active and up to date. Now there's no need to be anxious about the Fraud Alert, it's a method of putting the agencies on a heightened level of security and requiring any agency requesting your credit report to have a phone conversation with you first. This way you get a phone call before the thief is even able to open the line of credit. LifeLock also takes a few other actions such as removing you from several mailing lists for preauthorized credit card offers. Once signed up you're backed by $1 million dollars in protection against identity theft.
I wouldn't recommend the service if I didn't subscribe myself and believe it was worthwhile. Another good bit of information is that if you sign up to be an affiliate you can receive a 40% discount on the service.