Also worth knowing about is Microsoft's attempt at a Firebug clone: IE Developer Toolbar.

http://www.microsoft.com/downloadS/details.aspx?familyid=E59...

If you're working with IE Firebug Lite is also worth knowing about: http://getfirebug.com/lite.html

Anybody know of a plug in to tell if there are mismatched tags on a page? I can't seem to find one for firefox, my iPhone does it nicely in the error console :(

I don't know if the Firefox Error Console handles it (it detects CSS and JS errors fairly well) but the Web Developer toolbar has a shortcut to validate the current page.

I used to use Aardvark a lot, but I've found that Firebug basically completely supersedes it now. There used to be room for both, but I haven't used Aardvark in more than a year now.

I think Firebug replaces half the plugins he lists. Aside from it, the only other useful ones are color picker, web developer and yslow.

I just use digital color meter (mac) or colorpix (windows) instead of colorpix. Less browser overhead :-)