The value of the donation is the fair market value of the software, you may want to keep some kind of proof of how you determined that value, such as internet sales. And of course, the donation has to be made to a registered exempt organization and you should get a receipt.
One point I'm not clear on is the software license -- if the license does not permit you to give the software away, then the donation may be disallowed if audited -- you can't take a deduction if you don't have legal authority to donate the item.
