You select a swath of text from a Word document to transfer to a document in InDesign, and realize you can't Copy and Paste because you'll lose what's already on the Clipboard. You can transfer the selection using the Application Switcher instead.
Start dragging the selection in the Word document (move it a little bit and then stop). With the mouse button still down, press Command-Tab. Holding Command down to keep the Switcher open, drag the selection into the InDesign icon. You'll be switched to InDesign, where you'll see the usual "ghost" of a dragged selection, just as if you were dragging it within the InDesign document itself. Drag it into position and let go of the mouse button.
The target window isn't frontmost in the destination? Hang on to the selection by keeping the mouse button down, and press Command-~ (tilde) to cycle to the correct window. You can also use Command-N to create a new window as a drop target.
5. Hide and show background applications
You're in Pages. You can see only Finder windows in the background, and you want to refer to a Stickies note. You don't have move to background applications to rearrange windows or to hide them as you leave. Instead, press Command-Tab to open the Application Switcher, tab to highlight the Finder, and, with Command still down, press H to hide the Finder's windows. When you release the Command key, you'll still be in Pages.
Unhiding a background application is a little tricky because if you repeat this procedure (in this case, tabbing over to the Finder and pressing H), the background windows will reappear, but you'll also be switched into that application when you release Command. To make the windows reappear while keeping your Mac's focus in the current application, you need to press Command-Tab, tab to the application icon, press H to unhide its background windows, and then press Esc while the Command key is still down. Release the Command key and you'll still be in the original application.
6. Jump to an alphabetical Exposé
You can quickly trigger Exposé when the Application Switcher is on the screen by pressing the Up or Down arrow; you'll see the windows for whichever application was highlighted in the Switcher bar.
If you know the trick for arranging Exposé windows alphabetically—pressing Command-1—you'll be pleased to know you can jump right to this alphabetical arrangement from the Application Switcher. Instead of using the Up or Down arrow key to open Exposé, highlight the application you want and press the 1 key (you're already holding down the Command key). Hold it down for a couple of seconds. What's happening is that Exposé is triggered, and then it notices that Command-1 is being pressed and so offers the alphabetical arrangement—you'll see the windows swap into correct positions.
Bonus tip for trackpad users