The Minor Prophets: Haggai - Historical and spiritual overview of the Biblical prophet. - http://www.zianet.com/maxey/Proph9.htm
Haggai - Profile of the prophet from a joint Lutheran and Catholic bible study project. - http://www.aboutbibleprophecy.com/p18.htm
Book of Chaggai - The text of the Biblical chapters in Hebrew and English. - http://www.hareidi.org/bible/Haggai.htm
Catholic Encyclopedia: Aggeus (Haggai) - Commentary on the Biblical prophet from the traditional Catholic perspective. - http://www.newadvent.org/cathen/01209d.htm
Jewish Encyclopedia: Haggai - Overview of the prophet from the traditional Jewish perspective, including rabbinic commentary. - http://www.jewishencyclopedia.com/view.jsp?artid=63&letter=H