http://www.booksamaritan.com/

http://www.homeschoolbuyersco-op.org

Also, if you’d like to “trade” them for other types of books, or CD’s even, then look into Paperback Swap. HS curricula items go quickly there! For every book you send out, you’ll get a credit you can use for a different book (from any genre), or use it at the sister site, SwapACD.

http://www.paperbackswap.com

http://www.swapacd.com

You can also donate them to a local church library; many churches have listings for local home school groups they contact when these become available.

Or, you can post them on a curriculum site, and try to sell them.

This yahoo site seems to be very active in it.

http://groups.yahoo.com/group/1001books/