The next (draft) version of HTML is packed with exciting possibilities and features. It's also the cool new thing everybody does and well supported on most modern browsers.
You can read all the serious stuff at the semi-official website of HTML5.
Finally we can make websites that are no longer restricted by a narrow set of technial possibilities.
Websites can now be rich with subtle movement, smooth shadows and gradients and all the beauty a designer can dream of...
If you ever used a website, there's a good chance you used PHP. Major sites with functionality - like webshops or social network sites - are mostly driven by this server-side interpreted programming language.
There's hardly an end to what PHP can do (and for the rest I use jQuery to make it come true).
Due to its client-sided nature it is the ideal partner for PHP.