The United States Department of Labor provides a list of state-by-state tax withholding certificates at BLS.gov. For states with no withholding tax, copies of the federal withholding form can be downloaded from the Forms & Pubs section of IRS.gov
A federal W-4 — also called an Employee's Withholding Allowance Certificate — is a form created by the Internal Revenue Service to indicate to an employer how much money to withhold from an employee's paycheck for federal taxes, according to TurboTax. State W-4 forms function with the same purpose but measure the amount of money withheld from the employee for state taxes, rather than federal taxes.
The Internal Revenue Service lists more information about tax withholding at IRS.gov.