Skitch
Have you noticed how elegant yet obvious Skitch screenshots have become? For instance. I see them everywhere, and you can always tell it came from Skitch. Used to be that I'd have to open a blank web browser or something to serve as a backdrop for screenshots. Now I just need to make sure my wallpaper is suffficiently classy. Which is fine, I haven't seen my desktop wallpaper in months, I always have windows open.
Skitch still needs a 'blur' tool for anonymizing stuff, though..