HTML, it’s at the root of all web pages, (even flash sites) you cannot be a good web designer without knowing HTML
- FireBug
- Essential Firefox Addon for web development #1.
- Web Developer Toolbar
- Essential Firefox Addon for web development #2.
- 456BereaStreet
- One of the best Web Standards blogs out there.
- Sitepoint
- A forum for asking your CSS and HTML questions, also some good articles.
- XHTML: The Definitive Guide
- This is a good place to get started, and also something that you will be able to go back to throughout the years as you have questions
- bulletproof web design
- This book has some cool XHTML and CSS techniques that degrade gracefully
- Validate Your Site
- Validates your entire site (up to 100 pages anyway). You can also target directories to get the rest if you have over 100 pages.
- XHTML Character Entities
- By far the best reference for Character Entities
- HTML Email Design
- Some advice for HTML emails
- 24 Ways
- Similar to this page, 24 Ways is a collection of links to other tutorials.
- Digital Web
- Great online magazine for learning all kinds of web design techniques.
- Vitamin
- A online magazine for learning front end development techniques.
- HTML Form Security
- Techniques for improving the security of web forms
- More HTML Form Security
- Techniques for improving the security of web forms