Check it out, web developers, this is a handy tool for exploring / understanding / debugging web pages in IE, with features that enable you to:

• Explore and modify the document object model (DOM) of a Web page.
• Locate and select specific elements on a Web page through a variety of techniques.
• Selectively disable Internet Explorer settings.
• View HTML object class names, ID's, and details such as link paths, tab index values, and access keys.
• Outline tables, table cells, images, or selected tags.
• Validate HTML, CSS, WAI, and RSS Web feed links.
• Display image dimensions, file sizes, path information, and alternate (ALT) text.
• Immediately resize the browser window to a new resolution.
• Selectively clear the browser cache and saved cookies. Choose from all objects or those associated with a given domain.
• Choose direct links to W3C specification references, the Internet Explorer team weblog (blog), and other resources.
• Display a fully featured design ruler to help accurately align and measure objects on your pages.
• Find the style rules used to set specific style values on an element.
• View the formatted and syntax colored source of HTML and CSS.

Download it here, then visit the Developer Toolbar Wiki on Channel9 to provide your feedback. 

Wow!  How did I get along without it?  I can't believe I just discovered this, so I went to the Microsoft Downloads Notifications Signup page to make sure to get notified when new downloads are released.