Indeed, "thank you" is a powerful yet simple way to make a lasting impression. But you know what's as interesting? Is what does the receiver of the "thank you" say after you say thank you. Often you hear a response of "no problem," or if you're in Australia, "no worries." But a better response might be for the receiver of the thank you to say, "I know you'd do the same for me." This is a way of reinforcing or cementing the collaborative relationship at work.