When organizing and purging your clutter don't ignore your bookshelves and those piles of books on the bedside table. Ask yourself if you will read this book on a regular basis? Is it available at the library if you do decide to re-read it?
I decided that I will only keep a library of reference books for cooking and crafts that I often do. And I have a few favorites that I read one or two times a year.
Books are expensive and have a great deal of value; don't just give them away, first try to sell them. Amazon buys used textbooks, but I prefer to sell my books to Powells bookstore. Powells gives a store credit on books they choose to buy, which I find works well for gift giving.
Any books that I am unable to sell I donate to the library. They have a Friends of the Library bookstore that resells donated books for the benefit of the library. It's win, win all around.