HTML.com: Formerly HTMLCodeTutorial.com, this site was rebranded as HTML.com in September 2016. Not only does it have everything you could possibly need to know about HTML, the website design itself is quite lovely and clean. You don't have to plod through a bunch of ads to get the info that you need.
HTML Periodic Table: A simple and interactive HTML periodic table that helps anyone learn each tag with ease or get a quick reminder whenever they need it.
30 Beautiful Web Designs That Use Photos as Backgrounds
CSS-Tricks: Tips, a forum, videos, downloads... lots of goodies here.
Ultimate Resource list of Patterns and Backgrounds:
FreeGraphicsWorld.com: Royalty-free web graphics—buttons, bullets, backgrounds, page dividers, banners and templates.
GIF vs. JPEG Image Formats: When to use GIF and when to use JPEG, a basic rule of thumb...
HTML Cheatsheet: From Webmonkey.com, it contains the most common HTML tags and their proper syntax.
HTML Tips and Tricks, How-To and Beyond: An impressive array of HTML tips and tricks.
HTML Tutorial: From HTML.net, a free 15 chapter HTML tutorial.
Index of HTML 4 Elements: From www.w3.org.
The Ultimate HTML5 Toolbox: Links to all the best articles, videos, tutorials and resources on HTML5.
Using the Meta Tag: What are Meta tags, why should you use them, and how do you include them in your HTML.
Web Design Library: Free Web design tutorials, articles, news, interviews, Web design showcase and software reviews.
WebDevelopersNotes.com: Free online tutorials, tips, tricks, resources, graphics, designing, Web promotion, Web page design and Templates.
Webmonkey: Resources for web site developers including how-to guides, code libraries, server technologies and authoring resources.
WebsiteTips.com: Educational Web site design and development tutorials, tips and resources for Web site owners, Web designers, Web professionals and webmasters.
Working With Sound: How to add sound to your Web page using the BGSOUND and EMBED tags.