You can always sell them. Some of mine I sold back to my school. Others I put on Amazon. The payback is more on Amazon than ebay, at least in my experience.
The ones that I couldn't get any money for, as in I'd have to pay more for shipping than I would get for the sale price, I donated to my local library. The library will give you a tax receipt and you can write it off. Plus it gives you the warm-n-fuzzies :)