Changes in HTML5

There are lots of excitement about new HTML5 among developers. HTML5 is still under specification, and is currently in the Working Draft stage in the W3C, but many aspects of HTML5 are now stable and can be implemented in browsers

Document Type
The <doctype> for an HTML document has changed from its verbose DTD reference to a much simpler format, simply stating the document is an HTML document type:
<!doctype html>

Character Encoding
The <meta> tag for a document allows you to set the character encoding using the simple charset attribute, replacing declarations such as:
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<meta charset="UTF-8">

Script and Link Elements
The <script> element has been stripped down, removing the need for the type attribute. The reason for this is that scripts are typically written in JavaScript. The <link> element has lost its type attribute due to the prevalence of CSS.

Some of the new elements in html5 here:

<article> An independent piece of content for a document e.g. blog entry,forum entry
<aside> A piece of content that is somehow related to the rest of the page
<audio> Audio media content
<canvas> A component for rendering dynamic bitmap graphics on the fly. e.g games
<command> A command that the user can invoke: a button, radio button or checkbox
<datalist> Together with the new list attribute for the <input> element can be used to make combo boxes
<details> Additional information or controls that the user can obtain on demand, to provide details on the document, or parts of it
Used for plug-in content
<figure> A piece of self-contained flow content referenced as a single unit from the main flow of the document
<figcaption> Caption for a <figure>
<footer> Footer for a section; may contain information about author, copyright information, etc.
<header> A group of introductory or navigation aids
<hgroup> Header of a section
<keygen> A key pair generation control for user authentication in forms
<mark> A run of text in one document marker or highlighted for reference purposes
<meter> A measurement, such as disk usage, when the minimum and maximum values are known.
<nav> A section of the document intended for navigation
<output> Output such as a calculation done through scripting
<progress> Represents progress of a task such as downloading or performing other expensive operations
<section> A generic document or application section
<source> Used to specify multiple media resources on elements such as <audio> and <video>
<time> Date and time definition
<video> Video media content

NOTE: The input element’s type attribute now has these new attributes: color, date, datetime, datetime-local, email, month, number, range, search and tel.

The following elements have been removed from HTML5 because they are more effectively represented using CSS: basefont, big, center, font, s, strike, tt and u.

Other elements have been removed because they have a negative effect on usability and accessibility. These include: frame, frameset and noframes.

This last set of elements has been removed due to their lack of frequent use. They also caused confusion at times:
acronym (use abbr for abbreviations), applet (object replaces its use), isIndex and dir (use ul instead).