I frequently have more than one window open for a specific app. For example, I have my Thunderbird mail window, and then a new message is a separate window. When I command-tab through my apps (or use Expose to display all apps) it only shows the app, not the individual windows. If, for example, my new message ends up in the background, the only way I can get it back is to control-click on the Thunderbird dock icon and choose the window from the list. This is a pain when I'm working quickly and don't want to take my hands off the keyboard.
Is there any way I can get all open windows to show with a keyboard shortcut, rather than just the actual apps?