I'd like to give a big thanks to Marja Kingma (@Marjakingma) for introducing me to BookCrossing - a great way of sharing books you no longer need.
I can't remember who but someone also told me about BookMooch. But I think I prefer BookCrossing as it is less effort.
I have not started using BookCrossing yet - but I do have piles of old business magazines. Every time I go out, I take one with me and leave it somewhere such as a train or a cafe! Hopefully it gets read again before being binned and finally recycled!