Jewish Encyclopedia: Jonathan 
Overview of the son of Saul from the traditional Jewish perspective, including Talmudic commentary.
http://www.jewishencyclopedia.com/view.jsp?artid=398&letter=JCatholic Encyclopedia: Jonathan
Identifies four persons in particular of this name in the Old Testament.
http://www.newadvent.org/cathen/08499b.htm
Jonathan
Biblical biography of the steadfast friend of King David.
http://www.execulink.com/~wblank/20000521.htm
The Affection And Care Of Jonathan And The Contrivances Of Michal
Chapter on the devotion of David's friend and wife by the first-century Jewish historian Josephus.
http://www.interhack.net/projects/library/antiquities-jews/b6c11.html
