Microsoft has developed a very cool developer toolbar for IE (NOTE: it's still in beta).  If you do any sort of web development for IE you'll want this tool.  Sure, tools such as this have existed for some time, so it's nothing revolutionary, but it's definitely a nice addition to the debugging / analysis tools available for IE.

Using the toolbar you can explore the DOM, view element IDs and classnames, validate the HTML/CSS, etc.  Though simple at best I particularly like the resize feature where you can, with a single click, resize your browser to a particular size - especially helpful to test your webpage against a certain resolution.  It has a ton of cool features - it's definitely added to my toolset!

<grumble>You'll have to reboot after the install...I thought we were done with most of that.</grumble>