HTML 5 is the next big spec release of X/HTML and it has the web industry buzzing. XHTML was supposed to increment to v2, but got bogged down at the w3c and became a spec written in a vacuum of theoreticals. XHTML is now, for all intents and purposes, dead.
Hixie, at the WhatWG, took over the HTML 5 spec/name and has become the benevolent dictator of that spec. Because of this, we're seeing a light at the end of the revision tunnel.
HTML 5 will be the first specification created in the age of web applications, with all the baggage, and utilitarian needs, that brings with it. So far, Apple's Safari, Mozilla's Firefox, Google's Chrome, and Opera have managed to implement various portions of the spec and have already released versions of their browsers with some of those implementations available.
Google, for their part, is pushing HTML 5 into the world. Hard. Their Wave project has a beta of the Wave client in it's nth revision that relies heavily on some of the technologies found only in HTML 5.
HTML 5 brings new structural tags, draggable actions, a canvas element, media tags, and flexibility. All of these things make for an exciting view of the near-future of web development.
