Blue Web'N
A library of blue ribbon learning sites on the web.

W3Schools
Free Web building tutorials, from basic HTML to XML, Flash, JavaScript, and much more.

HTML Goodies
Primer, tutorials, references to a wide variety of web page creation related material.

WebDeveloper.com, ZDnet Developer, DevGuru and The Web Developer's Virtual Library
Webmaster's reference.

Writing HTML
A tutorial for creating web pages (by hand - in HTML).

The Bare Bones Guide to HTML
Lists every official HTML tag in common usage.

WebReference.com

Doctor HTML
A Web page analysis tool which retrieves an HTML page and reports on any problems that it finds. 

PageTutor.com
All sorts of HTML, Javascript and web authoring tutorials, from absolute beginner stuff to more advanced material.

Windows 95/98: winipcfg
Windows 2000: ipconfig /all

Internet Explorer Security Check