Immediately resize the browser window to 800x600 or a custom size.
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 objects on your pages. - Very handy
Though mainly a copy of what FF offer - its well worth the download and handy to have. Plus the ruler feature is pretty handy, and the DOM explorer is a nice way of drilling through your tags and elements to find any problems.