General References
Your Dictionary.com is an index of online dictionaries and thesauri, including speciality dictionaries for a number of professions. It is a great resource.
Merriam-Webster Dictionary and Thesaurus provides all the information you would expect from a dictionary and thesaurus, plus the site helps you add a button to your browser that will take you directly to the site.
The Wordsmyth English Dictionary-Thesaurus also combines the functions of dictionary and thesaurus in an integrated package.
iTools offers tools and dictionaries of many languages including computerese. Look to the menu on the left when you arrive.
Roget's Thesaurus is the standard print thesaurus and remains the same online.
Bartleby.com provides many reference books and encyclopedias, including Bartlett's Familiar Quotations.
The 1911 edition of the Britannica Encyclopedia is available online, and Britannica.com provides its 32-volume set online for free.
WhatIsIt is a site that answers that very question, not only for word definitions, but for computer terminology, acronyms, abbreviations, and almost anything that prompts you to ask: What is it?
Computer and MS Office Help
Microsoft Office Assistance Center is a site that provides references and tutorials for Word, Excel, Access, and all of the other MS Office products.
MicroSoft Free Stuff provides links to free downloads for those using Microsoft products.
Case Western Reserve University's A Beginner's Web Glossary provides a very complete glossary of internet terms.
The Internet Tour Bus is a free, on-going, semi-weekly, newsletter that explains the internet in plain English. There is a sign-up form at this site.
Web Wise is a site with an eight part tutorial covering important history and information about the Internet.
A useful reference for a Glossary of Internet Terms
World Wide Web Acronym Server is a dictionary of acronyms and abbreviations.
Business Writing
Business Letters: Accentuating the Positive is a quick summary of key ideas for writing successful business letters from the OWL at Purdue.
Kesseler Associates Online Marketing offers a good discussion of press releases for business.
12 Website Design Decisions Your Business or Organization Will Need to Make Correctly (or you'll have to do it all over within a year) by Dr. Ralph F. Wilson, E-Commerce Consultant, Web Marketing Today, Issue 126, July 9, 2003.
Upromote Article Archive contains a number of interesting articles conerning ways to promote your commercial site.
The Art of Business: Effective E-mail Marketing is an article explaining how to write marketing that doesn't look like spam.
Computer Science
The freecountry.com site offers free help authoring, manual, and documentation writing tools.
The IEEE Computer Society Style Guide provides editorial styles and standards used in the Society 's publications. These standards are also commonly used throughout the CIS field.
The ACM Portal to Computing Literature provides online access to many publications for the computing industry. This is a good research resource.
Medical Writing
American Medical Writer's Association: http://www.amwa.org/
Association of Healthcare Journalists: http://www.ahcj.umn.edu/
WritersWrite Medical Writing Resources: http://www.writerswrite.com/medical/
Science
Science Base: http://www.sciencebase.com/
National Association of Science Writers: http://www.nasw.org/
SciTech Daily Review at http://www.scitechdaily.com/, is an online journal of science with a wealth of information in many fields and links to additional resources.