Kapeli has released DockView 1.4.1 (http://kapeli.com/dockview/), an update of the Mac OS X app that extends the Dock and makes it aware of the windows that applications have open. The previews refresh constantly so you can keep an eye on windows without activating them.
With DockView, whenever a user points the mouse at an application’s icon, thumbnail images of the windows are displayed. The app helps Mac OS X users visualize the windows they currently have open and find the window they’re looking for. It’s also able to display the previews in the default Mac CMD Tab application switcher. Users can identify the application they are looking for and reduce the time it takes to switch between applications.
DockView requires Mac OS X 10.6.x (“Snow Leopard”). It may be purchased for US$7.99. The free version displays an alert every now and then and is otherwise fully unrestricted. Version 1.4.1 is a free update for registered users.