Deduction value of donations of used books to help fund ministry?

My ministry obtained 501(c)(3) certification from the IRS last year, and one way I am trying to help raise funds is by running an online bookstore selling primarily used Christian books. I have received several hundred books as donations since the beginning of the year since I started soliciting donations, and I'm hoping to go live with the store in a few weeks, but I'm not sure what I need to do as far as igning a donation value to the books when I send out donation receipts at the end of the year. Do I simply list the number and type of books donated and let the donor make the call on the value of the donation? Or does the IRS have any sort of a list of the deduction value of certain used items when it comes to charitable donations? Any links you could provide would be greatly appreciated.