The newest version of IE was released this week and some key features include embracing W3C standards more broadly, improved security and speed, along with backwards compatibility for pages created for IE6 or IE7.
One of the better improvements to this version, in my opinion, is the crash recovery system which makes each tab or window act as its own process so if one crashes the others are not effected.
You can learn about all the other new features of IE8 here