Domain Name Grabber is a free widget for OS X that lets you quickly and easily research domain names. Simply type in your idea and click “Go.” The widget supports dozens of extensions.
One might argue that there are online tools out there that provide better functionality. That’s definitely true, but Domain Name Grabber sits right on your desktop. You can even configure Expose on Leopard to open the widget upon moving your mouse over any corner of the screen. For the price of free, I’m not complaining.