Carl Sagan was definitely a great one. I watched most of his documentaries. "Billions and Billions" was a real treat.
On the subject of quotes... I'd like to share some of my favorites. I used to have these on my diary a while back.
Educational/Inspirational:
You tell me, and I'll forget. You show me, and I'll remember. You involve me, and I'll learn.
Great things are not done by impulse, but a series of small things brought together. - Vincent Von Gogh
Life is a hard teacher. First it gives you the test, then it gives you the lesson.
He who asks a question is a fool for five minutes. He who doesn't is a fool forever.
If I have seen farther than others, it is because I was standing on the shoulders of giants. - Isaac Newton
Only those who dare to fail greatly can achieve greatly. - Robert F. Kennedy
Romantic Quotes (Yeah, even I have a weak spot. ;))
Love is like playing the piano. First you must learn to play by the rules, then you must forget the rules and play from your heart.
I love you not for what you are but for what I am when I'm with you."
Things do not change, we change.
I have some funny ones, but they would spoil the mood after reading the above. :)