Federal laws allow the interception of tax refunds to enforce child support orders. Other methods of enforcement include wage attachments, seizing property, suspending the business or occupational license of a payer who is behind on child support, or -- in some states -- revoking the payer's driver's license. Your state's D.A. may employ any one of these methods in an attempt to help you collect from your ex. In addition, the U.S. Department of State may refuse to issue a passport to anyone who owes more than $2,500 in child support.
As a last resort, the court that has issued the child support order can hold your ex in contempt and, in the absence of a reasonable explanation for the delinquency, impose a jail term. This contempt power is exercised sparingly in most states, primarily because most judges would rather keep the payer out of jail where there's still a chance your ex will earn the income necessary to pay the support.
Almost every state has an agency that can help you with child support enforcement at little or no cost to you. For a list of links to these agencies, visit the National Child Support Enforcement Association at http://ncsea.org