TurboTax creators have an online free service called It's Deductable. It calculates what the value is and how much you are saving on your taxes. You can enter the items you are donating, mileage you drove to donate that stuff and print the list out. Then get a receipt from the charity where you donate and attach your list to it.
TurboTax® ItsDeductible Online - Track Charitable Donations for Tax Deductions.