If you're a Vista user, that odd sidebar has suddenly become relevant to your WoW lifestyle. Available for free from the Wndows Live site, WoW Explorer has a host of neat little plugins. The simplest of these features include the ability to put your realm on the Explorer skin -- you'll instantly be able to see if your realm is up or down, or what its population is like right now. You can also select your Explorer's theme, size, and toggle its docking behavior.
The Explorer's neatest feature, however, is the search functionality. The plugin lives on your Vista sidebar, which gives you instant search from your desktop. You can choose which popular site is the Explorer's default (such as your intrepid WoW Insider or maybe Wowhead), and the results instantly return in a flyout window. I ran several different searches, such as looking for Dual Specs or some different fat loot, and found the widget to be incredibly fast and responsive.
You can't beat the price at "free." Since I'm one of the masses who had previously stared at the sidebar wondering if the dang thing would have any use, it's nice to see something WoW-related live over my local weather widget.