General 

Making a Semantic Web

The Semantic Web - the original concept explained in an article by Tim Berners-Lee, James Hendler and Ora Lassila, in Scientific American, May 2001.

The Semantic Web: a primer - by Edd Dumbill.

The Semantic Web: an introduction - by Sean B. Palmer.

The Semantic Web, Universalist Ambition and Some Lessons from Librarianship, by Terrence A. Brooks.

SWAG - Semantic Web Agreement Group

The Semantic Web Community Portal

The Semantic Web In Breadth - an introduction to URIs, XML, RDF, schemas, ontologies and more general aspects of the Semantic Web, written by Aaron Swartz.

Semantic Web roadmap - an attempt to give a high-level plan of the architecture of the Semantic Web, by Tim Berners-Lee.

W3C Semantic Web - W3C is the World Wide Web Consortium, at the heart of the drive towards the Semantic Web.

 Tools and techniques 

Building a Semantic Web Site

KBS/Ontology Projects Worldwide - links to projects, tools, and events about ontologies.

Resource Description Framework (RDF) / W3C Semantic Web Activity

Semantic web & ontology related initiatives

Scientific publishing on the semantic web - by Tim Berners-Lee and James Hendler.

The DARPA Agent Markup Language Homepage - "The goal of the DAML effort is to develop a language and tools to facilitate the concept of the Semantic Web."

The SGML/XML Web Page - "... a comprehensive online reference work for the Extensible Markup Language (XML) and its parent, the Standard Generalized Markup Language (SGML)."

Web Architecture: Describing and Exchanging Data - an analysis of the XML Schema and the RDF Schema designs as used to further the semantic description of the web.