Go to System Preferences » Trackpad » More Gestures, and check the box to enable App Exposé. When you perform the gesture (swipe down with three or four fingers) in a supported app, you will see the expected Exposé behavior, but now you can also see a scrollable list of recent documents along the bottom of the screen.
This works with Apple apps such as iWork, Garageband, iChat, and Preview, and also with at least a few third party apps. I tested with Acorn and Pixelmator which both worked, but my copies of Adobe Reader and Sibelius 6 did not.
[crarko adds: Feel free to note other applications which do (or don't) work with this in the comments as you discover them.]

