In our new apartment we've only recently begun to use a new feature, one that we'd never encountered before, a Mr. Slim split-ductless AC system. Not totally attractive at first because these bulbous things are mounted high on the walls, we've been blown away lately at how damn powerful, efficient and quiet they are...
Made by Mitsubishi (Japan) and used widely in Europe and Asia, these units are newly showing up in the states and perfect for "new additions, retrofits, finished basements, and sunrooms" as the noisy condensing unit sits outside the home and only the air controller is inside. This means that when you turn it on, you hear NO MOTOR or anything, just the quiet flow of cool air. It's sort of weird.
We have one unit in each of the three rooms of our apartment (we're renters, the landlord installed these), and we use them in varying combinations with absolute glee, as they instantly pour cool air into each room and can easily be adjusted (with a remote) to regulate each room separately. This saves energy and allows us to keep our windows free of large noisy objects.
We tracked down all the information here: >> MrSlim.com