This little hint is hidden away in a video tip (Exposé Basics) on Apple's Exposé page, but strangely, isn't covered in the built-in Exposé help.
While in Exposé's All Windows mode (F3 or F9), pressing Command-1 will sort the windows alphabetically based on window name; pressing Command-2 will sort them by application name. Doing the same in Exposé's Application Windows mode will sort the windows alphabetically (obviously, sorting by application won't work in this mode).
[robg adds: Command-1 works as described in the video, but I'm uncertain as to how things are being arranged with Command-2 -- it doesn't seem to be alphabetical by program name on my Mac. I pressed Command-2, and wound up with this sort order (going left-to-right, three apps per row): Path Finder, Preview, Activity Monitor, Firefox, Terminal, System Preferences. I couldn't reconcile this order to either the order of the apps in the Dock, nor their order in the Command-Tab switcher. Anyone have any insight into the Command-2 sort order, or is my machine just behaving oddly?]

