For vehicles sold for $500 or less, you can claim the fair market value up to $500 without any additional paperwork. The preliminary tax receipt with the final sales price of your vehicle will be mailed within 5 days after the vehicle has been picked up.
If the gross proceeds from the sale of your donated vehicle exceed $500, your deduction will be limited to the actual sale price. You may deduct the sale price of your donated vehicle or the fair market value up to $500, whichever is greater. To get your deduction you must file an itemized return and provide your Social Security # and IRS form W-9.
You can find more information on charitable vehicle donation tax deductions at http://www.irs.gov/charities.