General

W3Schools Online Web Tutorials - a wealth of tutorials and references on various web authoring techniques.
Website: www.w3schools.com

World Wide Web Consortium - the international body responsible for web standards.
Website: www.w3c.org

AlistApart - excellent monthly magazine covering all aspects of web design and coding. All of their samples are free to use.
Website: www.alistapart.com

Firefox extensions - add-ons to firefox, many of which are a must-have for web development.
Website: https://addons.mozilla.org/firefox/extensions

Web Design from Scratch - varied collection of resources and opinion on many aspects of web design, including coding, graphic design, usability and information architecture.
Website: www.webdesignfromscratch.com

Dreamweaver tutorials - some basic dreamweaver tutorials.
Website: www.guidesandtutorials.com/dreamweaver_tutorial.html

EDCC - eDigital Competence Certificate.
Website: www.edcc.org.uk

Stock.xchng - huge collection of free, high-res stock photos.
Website: www.sxc.hu

HTML

w3schools XHTML Reference - complete reference of all html tags. Extremely useful.
Website: www.w3schools.com/tags

W3C validator - online html validator.
Website: http://validator.w3.org

HTML Dog - Some very useful html & css tutorials and reference.
Website: www.htmldog.com

HTMLplayground - quick and easy guide, with examples, of every html tag.
Website: http://htmlplayground.com

CSS

w3schools CSS tutorial - A good introduction to the basics of CSS.
Website: www.w3schools.com/css

w3schools CSS reference - complete reference of all CSS properties.
Website: www.w3schools.com/css/css_reference.asp

Maxdesign - large collection of CSS tutorials and recipes for building navigation menus and layouts.
Website: http://css.maxdesign.com.au

CSSplay - a collection of CSS demos, free to use.
Website: www.cssplay.co.uk

CSS cheat sheet - a bunch of useful CSS reference, on one sheet.
Website: www.ilovejackdaniels.com/css_cheat_sheet.pdf

CSS, Accessibility & Standards links - like it says.
Website: www.dezwozhere.com/links.html

Design

Web 2.0 how-to design guide - very good introduction to modern styles in web design. Website: www.webdesignfromscratch.com/web-2.0-design-style-guide.cfm

Design Meltdown - huge showcase of various sites, demonstrating different design techniques.
Website: www.designmeltdown.com

The Daily Slurp - another collection of nicely designed sites, updated daily.
Website: www.dailyslurp.com

CSS Zen Garden - the beauty in CSS design - loads of different designs applied to a single html file.
Website: www.csszengarden.com

Typetester - Compare different fonts for the screen.
Website: http://typetester.maratz.com/

Free photoshop exercises - very detailed photoshop lessons, in pdf format, with accompanying exercise images.
Website: http://www.oneil.com.au/pc/photoshop.html

Image file formats - quick guide to the different types of image file used on the web.
Website: http://www.yourhtmlsource.com/images/fileformats.html

Web 2.0 layer styles - some style presets for photoshop, free to download.
Website: http://www.dezinerfolio.com/2007/05/06/ultimate-web-20-layer-styles/