Defacto 2
Portal for the underground scene, covering all areas from gaming through emulation to arts. Included is a search engine, a scene portal, international news, a translator and hosted pages.
http://www.defacto2.net/

The Story So Far
An introduction to world of computer demos with pictures and links to further information, albeit partly biased towards the Atari ST scene.
http://mlab.uiah.fi/~eye/demos/

Scene.org
A site dedicated to the demoscene. At the moment it's oriented in demoscene productions, but promises to provide news, articles, interviews with demoscene people and up-to-date information about upcoming demoparties.
http://www.scene.org/

Pouet
Multi-platform database of news, groups and productions. Register here and get your own avatar and the chance to appear in a chart table which rewards uploading and commenting others' work. Nice, cute design.
http://www.pouet.net

Orange Juice
The demoscene information center, featuring news, information on people and parties, and a search engine.
http://www.ojuice.net/

Defence-Force: Demos page
Description of what demos are, some common effects, who makes demos. Available in English and French.
http://www.defence-force.org/computing/demo/index.htm

Introduction to Demos & The Demo Scene
Demos are cool. They exist to move you, just as any other art form moves you. But demos are built by programmers, artists, and composers who live and breathe technology. [Gamasutra]
http://www.gamasutra.com/features/20010216/scheib_01.htm

dEUS Demogroup
Official site of dEUS, the Greek demogroup, includes a member list, history, and productions.
http://www.geocities.com/SiliconValley/Sector/9242/

Demoscene Outreach Group
Builds awareness by presenting at the SIGGRAPH and Game Developers Conferences, as well as other events.
http://www.scene.org/dog/

256b.com
An archive of demos of 256 bytes or less.
http://www.256b.com/

The Hacker Demo Scene and its Cultural Artifacts
A paper that reports on a study undertaken into vernacular forms of multimedia production referred to as "demos" or "intros" and variants of these terms among adherents of a computer oriented subculture identifying itself as "the scene".
http://www.scheib.net/play/demos/what/borzyskowski/

Wikipedia: Demoscene
Encylopedia article, including history, development, and impacts.
http://en.wikipedia.org/wiki/Demoscene