Freecycle (books get snatched up quickly around here), mark them as free and put them out on the street, put them on the free table at the library, donate them to a women's shelter, see of you can leave them in a waiting room at a medical office, hair salon or garage, look for a bookcrossing drop-off, see if a used book store will take them (many won't take ARCs), if you attend a crit group or author meeting, give them away there, put them in a yard sale.
Ebay is a legal option but some authors will try to have the auctions pulled, even if it's an older release, because not everyone realizes it's legal to sell them so long as it's not a retail sale. I'd avoid a kerfluffle and use another option.