W-9: Request for Taxpayer Identification Number and Certification
http://www.irs.gov/pub/irs-pdf/fw9.pdf
W-4form: Employee’s Withholding Allowance Certificate
http://www.irs.gov/pub/irs-pdf/fw4.pdf
Form I-9: Employment Eligibility Verification
http://www.uscis.gov/files/form/i-9.pdf