You can peer into a zip archive and see which files are in there using the zipinfo Terminal command. You can refine the results to show you only the files with fgrep. You can take this same command and use it as a Shell Script in an Automator service for easy access. In this tutorial you'll also learn about using Shell Scripts with files as input arguments in Automator.
Does this work with disk image files?
Chris: No, as zipinfo only handles .zip files.