Sort of the same as "sunshine of the day"...I LOVE when people say, "You just made my day." Its rewarding to know that whatever small effort you just made actually changed someone else's day.
It may be an overused phrase, but I try to use it sparingly. Today, one of my vendors made a teeny exception to his company's policy to make my life a little easier. And I got to genuinely, wholeheartedly say, "Wow, thank you. You just made my day."
Cause he did.