Jewish Encyclopedia: Isaiah
Overview of the Hebrew prophet from the traditional Jewish perspective, including apocrypha and Talmudic commentary.
http://www.jewishencyclopedia.com/view.jsp?artid=261&letter=I

The Ascension of Isaiah
Discussion of this book of Jewish and Christian apocryphal texts about the life of the Biblical prophet.
http://www.jewishencyclopedia.com/view.jsp?artid=263&letter=I

The Isaiah Problem in the Book of Mormon
A critical analysis of Isaiah's role in the LDS holy text.
http://www.shields-research.org/Books/Sperry/Spry_Isa.html

LDS Scriptures: Isaiah
The prophet's role in the Book of Mormon and importance to LDS thought.
http://www.lightplanet.com/mormons/basic/bible/isaiah_eom.htm

Isaiah
Profile of the prophet from a joint Lutheran and Catholic bible study project.
http://www.aboutbibleprophecy.com/p21.htm

Prophecies of Isaiah
Twenty-one of the prophet's predictions, with biblical links and discussion about their fulfillment from a Christian perspective.
http://www.aboutbibleprophecy.com/isaiah.htm

Jewish Virtual Library: Isaiah
Detailed profile of the prophet, with links to pertinent Torah passages.
http://www.jewishvirtuallibrary.org/jsource/biography/Isaiah.html

Isaiah
Article about the Biblical prophet from an 1897 Christian source.
http://en.wikipedia.org/wiki/Isaiah