There is a huge amount of information online for the would-be web developer. Here are a selection that I’ve found useful:

Reference & Tutorial

W3Schools

An impressive array of tutorials about HTML, CSS, XML, and various other web-related languages. The tutorials are backed up with equally comprehensive reference material detailing every HTML element and CSS property (amongst other things).

HTML Dog

Patrick Griffiths’ nicely presented selection of tutorials are split into Beginner, Intermediate and Advanced sections. All stress the importance of web standards in building quality sites.

HTML Source

Another collection of great tutorial articles covering every aspect of building your site from the ground up. Written by Ross Shannon.

SSI Developer

Tutorials and guidance on using Server Side Includes (SSI) to incorporate content into pages, by “Enzo, an Irishman living in Finland”.

Articles & Blogs

Design PRINCIPLES

One-stop shop linking to new blog posts, interesting articles and generally what’s going on in the world of standards-based web design.

A List Apart

Online (free) magazine for web professionals, producing great articles on CSS and other matters.

Web Pages that Suck

Teaching good design by looking at bad design, Vincent Flanders shows what not to do on your web site.

Validators

W3C Markup Validator

The mother of all validators, this service checks that your (X)HTML is up to snuff, and tells you what’s wrong if it isn’t. Error messages have recently been improved for clarity.

WDG Validator

Another (X)HTML validator, this one allows you to validate a whole site at once. Great for catching isolated problems and slip-ups.

W3C CSS Validator

Once you’ve checked your page markup, check your stylesheets too!

Cynthia Says

Cynthia helps you assess the accessibility of your site, and its compliance with regulations such as WCAG and Section 508. Note that it is not possible to fully test against these standards automatically, but Cynthia does what she can and tells you what you’ll need to check with the human eye.

Site Report Card

All-in-one page checker that will validate a page, but also check for broken links, search engine placement, slow load times and even bad spelling.

Web Page Analyzer

Not strictly a validator, this tool will calculate the total “weight” of a page including all images, stylesheets, scripts, etc. and tell you where you can (and/or should) speed it up.

Other Resources and Tools

Free/Cheap Windows Tools

Twenty five inexpensive tools for fixing up your website, selected by Vincent Flanders.

The CGI Resource Index

A directory of thousands of CGI scripts, many of them free- or share-ware, arranged according to language and purpose.

Discussion Forums

Tek-Tips Forums

Not exclusively about web design, but a forum for getting technical questions answered in a wide range of fields. You are expected to answer some questions yourself if you want to use this forum long-term. Be warned, it can become quite addictive…

Google Webmaster Help

A place for webmasters to seek and share information about the way Google works (or doesn’t). Not without its trolls, but still somewhere where you can learn a lot about SEO.