Freecycle is a worldwide network of local groups who keep useable second-hand goods out of the landfill by connecting people with unwanted stuff and people who want the stuff. It's a brilliant concept. When I first came heard of it someone told me it was "like eBay, but free". However some people have become unhappy with the way Freecycle groups work in practice.
It's OK though. There are lots of other groups where you can advertise your unwanted used stuff and people will come and take it away to use it again.
Realcycle is one example. They operate in England, Scotland, Wales and Northern Ireland. Like Freecycle, they use Yahoo Groups to manage the mailing list, which some people think is a bad thing. My local Freecycle group just switched to Realcycle. That group has over 15,000 members which is a good thing - obviously the more members there are, the more interesting items that get offered, and the more possible takers there are for the used items you want to offer.
Freesharing is another group that uses Yahoo Groups. They have over 825 local groups with over 350,000 members in the USA, Canada and around the world.
Sharing is Giving also uses Yahoo Groups. They have groups in the USA, Canada, and a small number of groups in Australia, Scotland, England and Wales.
Here are some other free recycling groups I have come across. I don't know anything about them, but if you are looking for alternatives to Freecycle, you might find something in this list.
Worldwide Free Share
Freesources Recycling Network
Recycle 4 Free
Gift of Giving
Don't Dump That
Texas Recycle Network
Don't forget your local thrift/goodwill/charity shops if you have usable unwanted goods.
If you want to get rid of some books in a fun and environmentally responsible way, Bookcrossing is a really great way to do it. You leave a book in a public place - on a park bench perhaps - then you register the book with the bookcrossing website. An avid bookcrosser will come along shortly to pick up your book, and they may read it and post a review to the bookcrossing website, and maybe even leave it somewhere else for another bookcrosser to find. Or you could sell your unwanted books to your local second-hand bookshop.
If you have unwanted furniture, the Salvation Army might collect it to be reused by needy families. I know of various organisations near me who collect good used furniture for homeless people, victims of domestic abuse, asylum seekers and so on. There is a list of UK projects on the Sort It website.
If you don't want to give your used goods away but you don't want to throw them in the landfill, why not sell them on eBay or Craigslist?
The Sort-It website has more lists of places you can sell or give away unwanted used clothes, computer games, electrical appliances, bicycles and much more. So there's really no excuse to put serviceable stuff in the landfill. There are dozens of options for giving it away or selling it to be reused. What's more, you can probably find good second-hand alternatives to most of the things you might be thinking of buying new. And if you can't imagine why that would be a good idea - you need to go and watch The Story of Stuff.