Going through my daily blog feeds, I found a link to an old post on the IE blog. I don't know how I missed it before, but now I went ahead, downloaded, and installed the toolbar add-on. I can tell the toolbar is inspired by the Mozilla WebDeveloper extension by Chris Pederick: it has almost the same features. I use Chris' Mozilla extension all the time, and I am really happy I found an Internet Explorer counterpart.
The features that I loved:
The DOM viewer: this one is built in Mozilla. I have seen several bookmarklets that try to do it for IE, but this implementation is the most complete I have seen so far. You can select elements by clicking on them or you can search for them by tag name or id.
Element information: you can get the size of your images, the CSS classes and styles that are applied and more.
Clean browser cache: no more digging through two or more dialog boxes just to clear your cache. You can clear your cookies, session cookies, domain cookies with a single click too. Neato!
Validation: no more switching to Mozilla or Opera when you want to see if your page is XHTML compliant! You can do CSS and accessibility validation too. That is my favorite feature so far. You may already know that r.a.d.controls are XHTML compliant and W3C level A and above accessible. This toolbar will help us keep it that way easier.
Now I only have to see if the add-on plays well with Nikhil Kothari's Web development helper. There is no specific reason to believe the opposite, but I am trying to keep my browser add-ons to a minimum.