IETester is a free web browser allowing you to browse websites with the JavaScript & rendering engines of IE8 beta 1, IE7 IE 6 and IE5.5 on Vista and XP, as well as the installed IE in the same process.

You can also find a very nice tool for Internet Explorer named Debug Bar which includes a toolbar and a development bar +  a IE JavaScript debugger named Companion.js inside the same website.

It seems that canvas tag ( <canvas> ) will be very popular as it allows drawing graphics using scripting.

Canvas tag is supported in Firefox, Opera 9, Safari by default to allow 2D command-based drawing. But it is not supported by Internet Explorer.

ExplorerCanvas is a JavaScript that you can insert into your pages for bringing canvas functionality to Internet Explorer.

To get the ExplorerCanvas, click here.

For more details about the canvas tag, click here.