I’ve known since the early days of having a MAC that I can take screenshots using: ⌘ + ⇧+ 3 to take a fullscreen shot and ⌘ + ⇧ + 4 to take a selected area screenshot.

What I did not know (until moments ago) was that ⌘ + ⇧ + 4 + SPACE will grab a screenshot of a selected window. Exciting, isn’t it?