Generally, textbooks and encyclopedias are quickly outdated and are not accepted by most resellers or libraries. Call before dropping off either textbooks or encyclopedias.
Other paperback and hard cover books (ie. fiction, history, biography, etc.) may be reread and have a long life.
Consider donating to your local library or one of the following:
Paperback Books: Recycle with regular paper recycling or Keep Northern Illinois Beautiful Recycling Center
Hard Cover Books: Only the pages are recyclable. Covers should be removed and disposed of.