What a good initiative. There's no excuse for books going to landfill, not in the UK anyway. Give them to a friend or take them to a charity shop. If books are in poorer condition, charity shops will send them to recycling rather than landfill - I suspect a lot of out-of-print books are being lost that way, but it's still better than chucking them in the landfill. You can also take them to a book recycling bin or Better World Books bin, if you have access.
Talking of libraries, I visited mine today for the first time in a couple of years. Seeing so many of my purchases available for free was a guilt trip, but, oh, it was bliss to wander around! I now have The Silence of the Girls by Pat Barker and Pure by Andrew Miller lined up to read (thanks @Leonora for mentioning Pure).