http://getfirebug.com/lite.html
Version 1.2 of Firebug Lite contains more than just ‘console.log’ from the previous version. It tracks AJAX calls, inspects DOM elements and shows you the HTML, CSS and JS code. Definitely an improvement.
There’s a bookmarklet on this page that you can drag to your Bookmarks bar in IE, Opera, Safari (and Firefox, if you wanted to) which will spawn Firebug lite at the bottom of the web page.
Might be worth dragging that bookmarklet up to the top of your browser!