What to do with a bunch of books?

So Erica and I have been cleaning out our spare room, turning it into the baby's room. We've done a pretty good job. There are still filing cabinets and a few other things, and a bookshelf full of books that need to be gotten rid of.

These are the expensive books that we didn't resell to the bookstore - the ones we felt would be worthwhile to keep. Well, it turns out that after sorting through my books, I only really want to keep half of them, or less. We would like to not simply put them in the dumpster.

They're likely to be a few revisions behind the current. You know how that is - publishers change a word and come out with a new version every other semester, to keep students buying brand-new books. We're wondering if the book-buy-back places will buy them. We could put them up on half.com, but that's almost more trouble than it's worth, between running to the post office and dealing with people who for whatever reason are unhappy and want to give you a bad rating. Another possibility we've wondered about is donating them to a library for a tax break.

Have any y'all already ran into this? What did you do?