Web Developer Toolbars

I have found the following developer toolbars invaluable during web development. Some of them you might be aware of alreay, but some of them might be new to you.

Internet Explorer
<ul>
<li>Internet Explorer Developer Toolbar</li>
<li>Web Development Helper</li>
</ul>Firefox
<ul>
<li>Web Developer</li>
<li>XML Developer Toolbar</li>
</ul>