Joel's Humanistic Blog is also helping to organise a blog-a-thon on Sagan's life and work. He has posted a useful list of Sagan-related material online.
And then there's the man himself:
'The truth may be puzzling. It may take some work to grapple with. It may be counterintuitive. It may contradict deeply held prejudices. It may not be consonant with what we desperately want to be true. But our preferences do not determine what's true.' 'Wonder and skepticism', Skeptical Inquirer, 1995
I'm far from a Sagan expert, but I have very fond memories of watching him on TV when I was a young boy (mostly public television). I still think of him sometimes whenever I say the word 'billions'.
So, let this small comment (and link to people who know more than I do) stand as a humble contribution to remembering him.