Mozilla, Opera, and Apple are pushing the W3C to recognize their proposal for HTML 5, the first large upgrade to HTML since 1999. You can read more about it here.
The HTML 5 specification includes some really cool stuff: Web Apps 1.0 and Web Forms 2.0. Web Applications 1.0 adds new elements to HTML and DOM to provide a richer environment in which to build on-line applications. For example, Web Apps 1.0 will allow you to present a context menu when the user right-clicks on an element, and you can draw a line connecting two points on the browser screen. Web Forms 2.0 (not to be confused with XForms) adds some powerful features to make controlling and processing user input from web forms a little easier. For example, you can more easily specify what types of characters are acceptable in a textbox or indicate that the form values are to be submitted as an XML document.
HTML 5 is designed to be backwards compatible, so the billions of pages which have been written with previous versions of HTML will still display correctly in newer browsers supporting HTML 5. This is a very important and positive development from a preservation standpoint, and it will likely help HTML 5 be adopted more readily by the development community.
Of course the most important player to get onboard is Microsoft who still controls around 75% of the browser market. Microsoft is busy right now promoting XAML, so it may not be in there best interest to devote many resources to HTML 5.