Locate a computer recycling center in your community- Sometimes recycling monitors can be costly so if they are still in working condition donate them to a non-for-profit in need-, In my previous position of working for a non profit we dontated our old computers to "habitat for humanity restore"- - Good luck

We remove the hard drives for security's sake and list them for sale them on publicly available sites, such as eBay and Craigslist.