OK, so it's not as good as the genius that is Firebug (which runs inside Firefox), but if you want to see what's happening in IE when testing your web app then you'd best head on over to the Microsoft web site and pull down the official Version 1.0 release of the IE Dev Toolbar.

The IE Blog also has a little more information on it, including a video of Steve Ballmer getting emotional again - not quite as bad as the Dancing Steve video but still pretty funny (rendered with Silverlight of course).