Something I discovered recently is Leopard’s screen capture functions.
Anywhere in the OS, if you press Command-Shift-3 you’ll get a nice full screen capture of your desktop, if you use Command-Shift-4 the cursor changes to a little marque tool which you can use to mark out a spot to capture. And the pièce de résistance is Command-Shift-4 and then press spacebar. This changes the cursor into a little camera that highlights GUI elements and windows. The coolest part of this is that for transparent objects you don’t capture what is behind the element and the screen capture also includes nice drop shadows and the like. Very cool.