Sagan's series "Cosmos" was what really brought him into the public eye, and certainly remains the strongest impression of him for me. He was able to do with science what many of us SF writers try -- and often fail -- to accomplish: create a true Sense of Wonder, sometimes just by an image of his OWN wonder on the screen. He was also one of the strongest voices against what he saw as an overpowering wave of mysticism and fuzzy thinking.
There are few like Sagan now, and never have been many, and never will be, because it takes a very special kind of man to do what he did and do it well.
I have saluted him as best I could in my own way; Nicholas Glendale, the famous scientist character in "Boundary" and its forthcoming sequel, is very consciously and strongly based on Sagan. I like to think that, if he were alive, he'd have enjoyed knowing that.