If you are one of those users who tested Windows 7 beta, you will know that one of the most handy feature is that we can reorganize the tabs in the taskbar. Sadly this important feature(that increases productivity) lacks in older version of Windows, i.e XP, Server 2003/2008, and Vista.
Taskix is a free tool that adds the ability to move and reorder the taskbar tabs easily. Simply drag the tab that you want to move and it will reorganize itself. It is a robust program that has a very small memory footprint. And yes, it supports multiple monitors too.
Run the program and you will see all options listed in a single window. By default only one feature is enabled, i.e dragging tabs to reorganize them. You can enable other features as well, such as, Scroll and reorganize tabs with mouse wheel, Maximize or close the tabs with middle mouse button, Enable support for multiple monitors, Auto-start in Windows, etc.
It is available for both 32-bit and 64-bit versions of Windows. It is small, simple, and very effective. Enjoy!