I always try to donate old unwanted books.

We use the library for reading and donations, exchange & donate books on BookMooch, share with friends, and repurpose childrens books for art projects. We do this primarily if a book is damaged, but its art can be used for something fun. It can also work with regular books that may have been damaged in some way as gift wrap or packaging.

Use your local library. Find out what it has to offer, from ebooks and online databases that save you money to the newest bestsellers in books and music.

Donated clean & still readable books are often the main fundraiser for Library Friends' organizations so be sure to check with your local library when weeding your home or office book collection. Shop at these library sales for more recycled books to read & collect! These auxilliary funds are badly needed by libraries in these days of reduced funds for local public services. The largest amount of support for Public libraries comes from local city & county funds.
Also, I belong to an Altered Art group that uses books as the platform for mixed media & collage art.

I donate my books to the library. They can use them in the library or sell to obtain other materials they're in need of.