Various sites to download free W9 forms.

The W9 form is used by employers of independent contractors to obtain the information that they will need in advance to later be able to send a Form 1099 for money paid for the contractor's services. A 1099 must be used for money paid out to a contractor in the amount over $600.00 as of 2011.
The 1099 allows the employer of the contractor to deduct the amount from the employers taxes.

www.printw9.com

www.downloadw9.com

www.rc123.com/w9_print.html

www.rc123.com/w9_print_spanish.html

www.w9form.biz

W4 Form

Use this to tell the IRS how much your employer ill deduct from your paycheck for the taxes that will be due

www.w4form.biz

1099 Forms

This site www.1099Forms.org is the authority site on the subject.

W8 Form

There are several W8 forms for different purposes used for foreign people dealing with the US IRS.
Read the W8 Instructions before you use any W8 form.

W8 Instructions

W8-BEN Form
Certificate of Foreign Status of Beneficial Owner for United States Tax Withholding

Publication 919 - How do I adjust my tax withholding?

Publication 17 - Your Federal Income Tax (For Individuals) 2011

Publication 17 - Your Federal Income Tax (For Individuals) In SPANISH 2010