Peter Grant (no link because it disappeared) had a page of Great Science Fiction Quotes in his blog. I can't pick just one as a favourite. Here are some:

“There’s no real objection to escapism, in the right places… We all want to escape occasionally. But science fiction is often very far from escapism, in fact you might say that science fiction is escape into reality… It’s a fiction which does concern itself with real issues: the origin of man; our future. In fact I can’t think of any form of literature which is more concerned with real issues, reality.” – Arthur C Clarke

“Isn’t it interesting that the same people who laugh at science fiction listen to weather forecasts and economists?”

“Science fiction writers foresee the inevitable, and although problems and catastrophes may be inevitable, solutions are not.” – Isaac Asimov

 

“Experience comes from doing, not from being told. Experiment and discover. Seek and find. It is not machinations of others that compel us to do so; it is our need to know. It is, in the end, the way we learn.” – Terry Brooks, The Talismans of Shannara

 

“A neat and orderly living space is the sign of a dangerously sick mind.” – Mercedes Lackey, The Black Gryphon

 

“Reality is the part that refuses to go away when I stop believing in it.” – Phillip K. Dick