(X)HTML Hypertext Markup Language
Apache The Apache webserver. Sorry, I don't have any experience with IIS or any of the others.
Blogging Be a blogger. See the RSS section too.
Color Color schemes
Content Management Systems Easily manage your content with these systems :)
CSS Cascading style sheets, separation of church and state- oh I mean separation of content and presentation.
Customer service / Support Providing support, customer service & help to your customers
Design, Style & Useability Create usable sites for a modern age :)
DNS Domain name servers
Domains Domains, registration & transfers.
ECommerce Selling / buying things
Editors & IDEs Text editors, & integrated development environments for web development.
Firefox Extensions Firefox extensions that are helpful to webmasters
Fonts
Forum Software Have a community
Freelancing Find freelance programmers, designers, translators etc. Or find work :)
FTP / SSH / Telnet File transfer & server connections/control
Google Google gets its own section :)
Graphics Tools for creating/manipulating images & sources for images
Hosting Got to have someplace to host. Of course there are hundreds of other hosting companies, but these are the best (subjective of course).
Javascript / AJAX Javascript is not Java, and the ubiquitous AJAX is Javascript.
JS WYSIWYG Editors Javascript editors to place on your pages or in your web app.
Mailing lists / Listserv Manage mailing lists & Listservs. The ones marked "Listserv" are for email discussions among many users, the others are for you to email to the list.
Maintenance Keep your site in tip-top shape
Mobile accessibility Stuff to help you make your site accessible to mobile (phone, pda etc) users
Monetization How can you make money with your website?
Perl Larry Wall's dynamic programming language.
Php Php the web programming language
Promotion Get the word out about your site.
Python Google's favorite programming language.
Reg Ex Regular Expressions
Robots / Spiders / Search Handling robots or adding search to your site
RSS/Atom feeds Learn about syndication. See also the blogging section. RSS => RDF Site Summary / Really Simple Syndication.
Ruby / RoR Ruby is a programming language, Ruby on Rails is a simple open source web application framework written in Ruby.
SEO / SEM Search Engine Optimization & Marketing & Online marketing / promotion in general
Servers Servers and server administration stuff. See also the Apache section.
SPAM Dealing with SPAM
SQL All about SQL (mostly MySQL-specific stuff)
Statistics Server stats can be really useful
Tcl Tcl, Tcl/Tk
Tools There are lots of tools that didn't seem to fit in the other categories
Tutorials, Examples, Code & Reference This is for sites that have lots of examples and tutorials, but don't fit into one category for JS, CSS, Php etc.
Validation, Cross-browser checking Make sure it validates and works in most browsers. See also the Mobile accessibility section for phone/pda-specific validators.
WebDAV Web-based Distributed Authoring and Versioning (Thanks Dan M. for suggesting this)
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