Apple’s page on HTML5 and Web Standards as supported by their Safari 5 web browser.
Lots of background information and examples related to the various modules that make up CSS3.
Provides royalty-free fonts in various formats suitable for distribution on the web.
The actual HTML5 specification at the W3C
HTML5—Mozilla Developer Center
Mozilla Developer Center’s page on HTML5.
Implementing Web Socket servers with Node.js
How to write websocket servers with Node.js.
Microsoft IE9 Test Drive
Demonstrations of HTML5 (and related) features in Internet Explorer 9
Ruby and Websockets—TCP For The Browser
Information on em-websocket, a Ruby library for building web socket servers.
Setting Up A Flash Policy File
Contains a detailed description of Flash Socket Policy files.
Unit Interactive: Better CSS Font Stacks
Discussion of font stacks, with some excellent examples.
Video For Everybody!
Information on HTML5 video, with code to play video on all browsers.
When Can I Use…
Browser compatibility tables for HTML5, CSS3, and related technologies.