Typography

@font-face

Web designers are limited to a handful of cross-platform specific fonts:
Arial, Comic Sans MS, Courier New, Georgia, Times New Roman, Verdana.
@font-face brings with it the hope of a standard, cross-platform, cross-browser, lightweight method for referencing font-files not found on end users' computer.
In other words: it allows web designers to store fonts on their server and reference them in CSS, regardless of what fonts the user browsing the page has installed.

Multi-Media

Voice Recognition

WAMI (Web-Accessible Multimodal Applications) is a project out of MIT that lets you plug voice recognition directly into a javascript powered page, and optionally record+save audio files of people talking.

Graphics

Canvas

The canvas element is one of the most exciting features of HTML 5. You use JavaScript to draw whatever you need on this (literally) blank canvas and can dynamically generate graphics that support your content.

SVG

You can embed SVG (Scalable Vector Graphics) vector-drawn art, in your documents, for Firefox browsers.
SVG Web is a JavaScript library which provides SVG support on many browsers, including Internet Explorer, Firefox, and Safari.

WebGL

Brings 3D graphics into web browsers natively and lets you draw things into a 3D context of the canvas element.