The Internet 
- Entering the World Wide Web: A Guide to Cyberspace
- Internet - John December's list of sources about the Internet
- WWW and Internet Manuals
- EFF's Extended Guide to the Internet - (formerly The Big Dummy's Guide to the Internet) This material will be published by MIT Press, called Everybody's Guide to the Internet and would be much more readable in hardcopy.
- Short History of the Internet - (short if printed out, not so short to read online)
- Internet Timeline - a chronological timetable of the development of the Internet
- How to Search the Web: A Guide to Search Tools
- Beyond Surfing: Tools and Techniques for Searching the Web
- Boolean Searching on the Internet
- Choose the Best Search Engine for Your Information Needs
- How to Choose a Search Engine
- Evaluating Internet Information
- HTML Made Really Easy - As it says - quick and easy with many clear examples.
- Writing HTML: A tutorial for creating WWW pages - learn how to design Web pages using on-line lessons. Well done and easy to follow.
- HTML quick reference
- Bare Bones Guide to HTML - A concise "cheat sheet" that can be used to look up basic syntax.
- A beginner's guide to HTML - Comprehensive, but very long.
- Crash course in HTML - A cute feature here is the little quiz after the tutorial.
Number Theory 
- Prime numbers
- The Prime Page - An Index of Information on Prime Numbers
- A survey of the theory of error-correcting codes
- Binary representations of data
- Mathematics Archives - Numbers
- Mayan math
- Data Index FAQs Short explanation of various coding schemes, from a company that manufactures bar code labels, verification equipment and such.
- Barcode history and explanation Click on the questions under "All about barcodes" for a brief history and explanation.
- Generate the bar code for a given UPC number -- cute!
- UPC database - Enter a UPC and look up the product.
- NUMERICON: a number museum
- David Wright's list of useful mathematical resources (loads of pointers here!)
- Using RSA public key cryptography for Internet security
- Prime numbers - A historical overview of the study of prime numbers, with links to biographies of mathematicians.
- Largest known values of various types of primes
- UPC Code Council - organization that assigns UPC codes to companies
- ISBN agency - organization that assigns ISBN numbers to publishers
JavaScript 
- Yahoo's JavaScript site
- Netscape's JavaScript Guide
- Netscape's JavaScript Reference
- 30-Step JavaScript Primer by Joe Burns
- Voodoo's Introduction to JavaScript
- Thau's JavaScript Tutorial (in 5 lessons)
- Short JavaScript tutorials on specific topics
- JavaScript Learning Center (14-lesson tutorial)
- JavaScript for Beginners
- Ask the JavaScript Pro - JavaScript questions and answers
- JavaScript Tip of the Week Repository
RGB Color Codes 
- Lynda's Color Chart - find the color you want and copy the RGB values off the box.
- ColorCenter - a nice interactive page that allows you to click on a color and see what it looks like on a large page. Change the setting in the upper left corner from "Hex" to "Dec" to get the RGB values to use in your Java code.
- RGB code converter - Allows you to enter different color codes and preview the color.