My absolute favorite is in my signature. I doubt Tyson really meant it that way, but to me it's a perfect metaphor for the grind of human experience.
Another favorite is from Carl Sagan...
"To make an apple pie from scratch, you must first create the universe."
At first it's just a good chuckle, but upon further thought I think it's a really nice meditation on man's failure to consider the world outside his own frame of reference.
What are some of your favorites?