Forms You Will Need
W-9: The IRS requires you, the business owner, to have a form W-9 for any subcontractor who provides a service for you. These are used to generate 1099s at the end of the year. You also need a W-9 for anyone who provides a private loan to you in order to reported claimed interest and for anyone to whom you paid commercial rent in order to report the rent payment expense.
W-4: A W-4 is required for every employee. The w-4 is used to calculate both State and Federal withholding taxes and in Colorado for required new hire reporting.
I-9: The federal government requires an I-9 for every person in your employment (including you). In the state of Colorado your completed I-9s must be accompanied by photocopies of the identifications reported in section 2 of the form. It is highly suggested I-9s be kept in a safe location separate from the employees file. They also must be available upon request to government auditors. For more information check out I-9 Central http://www.uscis.gov/i-9-central E-Verify even has a handy desktop widget: http://www.uscis.gov/i-9-central/form-i-9-desktop-widget-landing-page