One of the features I’m excited about in Windows 8 is the built-in multi-monitor Taskbar support. Microsoft finally got around to adding a Taskbar that stretches across all of your monitors, but for people running another version of Windows can always fallback to the free ZBar utility that does the same kind of thing.
ZBar adds pretty much all of the features you’d expect from an app like this, and from my point of view it competes quite well with paid alternatives such as Ultramon. The thing I really like about ZBar is that it is truly an all-in-one multi-monitor tool because of the included wallpaper manager. Most of the apps that are able to stretch a Taskbar across all of your monitors are capable of doing just that, but ZBar also lets you manage the desktop wallpapers that appear on each of your monitors. You can set a different image for each of your monitors, or you can stretch a nice panoramic across all of them.
If you just have a single monitor this kind of app won’t due you much good, but for everyone else something like this can definitely make you more productive.
ZBar Homepage (Windows only; Freeware)