From the “why isn’t this built in to Windows already?” department:
Taskbar Shuffle is a small, free program that lets you move not just items on the taskbar, but icons in the system tray (by the clock) as well. It also has a few grouping tweaks and also allows you to close taskbar items with a middle-click.
I’m only reporting about this now because the author only recently released a version that works on x64 Vista. I’ve been using it for a few weeks now, and I just love it.
Read more about it (or download it) here.