1. Contact one of the three credit bureaus and ask that an extended fraud alert be put on your account. This will require all creditors to contact you directly before granting any new credit in your name. The bureau you contact will share this information with the two other bureaus. The fraud divisions can be reached at:
2. Contact your local police department and ask to file a criminal complaint. Some police departments aren't too thrilled to do this, since it is a very difficult case to pursue. But be persistent; simply having the complaint document is going to help you deal with cleaning up your reputation with creditors.
3. Complete the Federal Trade Commission's ID Fraud Affidavit and submit it to all creditors where you have an ID Theft dispute.
The Privacy Rights Clearinghouse has a ton of helpful advice on dealing with identity theft.