The SGML/XML Web Page

Database containing over 2000 documents pertaining to SGML, XML, and related standards. Features a bibliography for SGML, vendors and service providers, software reviews, mailing lists, user groups, and projects.
http://www.oasis-open.org/cover/sgml-xml.html

Graphic Communications Association

Supports and promotes SGML and related technologies in their efforts in advancing interoperability of information systems.
http://www.gca.org

Overview of SGML Resources

SGML links at the W3C, meant for use in reviews of the HTML specification.
http://www.w3.org/MarkUp/SGML/

SP

A free, object-oriented toolkit for SGML parsing, validating, and entity management.
http://www.jclark.com/sp/

SGML on the Web

Circa 1995 list of SGML web sites, and resources for using SGML on the Web.
http://www.ncsa.uiuc.edu/SDG/Software/Mosaic/WebSGML.html

Women Writers Project, ACM Crossroads Winter 1999

This article from Crossroads Winter 1999 issue describes the use of SGML to encode literature archives for research, written by B. Fan.
http://www.acm.org/crossroads/xrds6-2/women.html

Comparison of SGML and XML

A Note from the W3C detailing the differences and similarities between the two markup languages.
http://www.w3.org/TR/NOTE-sgml-xml

A Gentle Introduction to SGML

An SGML FAQ in the context of the TEI e-text initiative and SGML application.
http://www-sul.stanford.edu/tools/tutorials/html2.0/gentle.html

SGMLtools-Lite

Formerly Linuxdoc-SGML, SGMLtools offers a out-of-the-box SGML processing solution for technical (DocBook) documentation. [Open source, GPL]
http://sgmltools-lite.sourceforge.net/

SGML: A Gentle Introduction

Tutorial from Text Encoding Initiative.
http://etext.virginia.edu/bin/tei-tocs?div=DIV1&id=SG