Style Guide for Online Hypertext - http://www.w3.org/Provider/Style/Overview.html Defines common terms and outlines good design principles.
Writing Well for the Web - http://www.webreference.com/content/writing/ Internet-specific copy writing tips for non-writers. Covers common mistakes.
Yale Web Style Guide - http://www.webstyleguide.com/ A manual covering graphic and information design, page layout, graphics, site navigation, and multimedia content.
Writing - http://alistapart.textdrive.com/topics/content/writing/ An index to A List Apart's articles on writing, style and usability.
Information Design - http://www.informationdesign.org/ Digest of knowledge on interaction design and information architecture, including the web and new media.
Cyberfrem - http://homepage.ntlworld.com/cyberfrem/guide/ Offers basic guidance and advice on designing effective, usable, easily navigable web sites.
What is Good Hypertext Writing? - http://kbs.cs.tu-berlin.de/~jutta/ht/writing.html There is more to writing than putting words next to each other, and there is more to writing hypertext than throwing together a bunch of links. By Julia Degener.
Stylegala - http://www.stylegala.com/ A showcase of graphic design for the web. Particularly supports coding standards.
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