Namecat.com has a really cool widget for the MacOSX Dashboard.
Domain Name Grabber is a widget that allows you to check if a domain is available directly from your Dashboard. It actually launches you to Namecat just like running a whois on a domain. It doesn’t really run a query except sending a browser query string. While this is useful, it also means that it doesn’t show up directly in the widget which would definitely have made it more powerful.