Gary Pretty has a detailed post on some of the new features in Expression Web 2 - I hadn't realised there was so much goodness in it!
Gary lists the following:
PHP Support - PHP Intellisense and syntax highlighting, and previewing of PHP sites locally, without the need for a separately installed web server
ASP.Net & AJAX Controls - full support for the standard ASP.Net Ajax controls to simply drag and drop them into your page
Silverlight 1.0, Windows Media & Flash - drop your Silverlight 1.0 applications straight...