Eyes and Ears
Eyes and Ears is a book of melodies for use in practicing sight-singing. You can download it for free. It currently contains about 400 melodies, arranged systematically for education. So far, I've concentrated on assembling a body of relatively easy material that would be sufficient for the first semester or two of a college-level musicianship course. There is a small amount of didactic text, but if you're going to use the book for self-instruction, you'll need some background in basic music theory, and preferably access to someone knowledgeable to provide guidance.
The book's home page is here: http://www.lightandmatter.com/sight/sight.html