This is one topic that Rick Mendosa does better than I could ever hope to.  
Please follow the below links and select those articles that help you the most.

Diabetic Information By Rick Mendosa
    Discussion of GI: http://www.mendosa.com/gi.htm

    Actual GI food lists: http://www.mendosa.com/gilists.htm

    Books that can be ordered about GI: http://mendosa.com/reviews_books.htm

    Diabetic Information By Rick Mendosa - This is the best site I have ever seen - Valuable information!
    http://www.mendosa.com/diabetes.htm