John Scalzi, author of many ultra-awesome books including Old Man's War and The Android's Dream (which I'm currently reading and massively crazy about) is one of those rare SF authors who can write about the science as well as he writes the fiction. His Rough Guide to the Universe is a great astronomy gook for noobs and backyard astronomers alike, and his blog The Whatever is on my short list of daily reads.
I'm still a great admirer of Carl Sagan, primarily because he did something I see as immensely important: he popularized science and with patience and good humor brought into people's homes. He did it through Cosmos, most obviously, but he also did it every time he popped up on The Tonight Show and talked with celebrity fluidity about what was going on in the universe. He was the people's scientist. This is not to say that you'd look at Sagan and see him down at the NASCAR race; it is to say that he could easily use a NASCAR race to explain, say, relativistic speeds and what it means for traveling through the universe.
This is important stuff. Getting science in front of people in a way they can understand -- without speaking down to them -- is the way to get people to support science, and to understand that science is neither beyond their comprehension nor hostile to their beliefs. There need to be scientists and popularizers of good science who are of good will, who have patience and humor, and who are willing to sit with those who are skeptical or unknowing of science and show how science is already speaking their language. Sagan knew how to do this; he was uncommonly good at it.
I read this earlier today, and I'm so intimidated by following it (and all the other tributes) that I'm totally going to cop out and just point you all to John's blog. It's a great tribute to Carl Sagan, and (for me, at least) serves as a call to arms for those of us who love and respect science: there's a dedicated effort right now to marginalize and even subvert scientific research and the scientific method (lead, big surprise, by The Decider and his merry band of whackos) and we desperately need someone like Carl Sagan to bring us something like Cosmos, so more people can understand why science matters, and why it's worthy of our respect and attention.
As Sagan said, "I don't want to believe. I want to know."