"Freedom is what you do with what's been done to you."
I quite like the defiance in that. Not mad keen on Sartre generally - much prefer the humanity of Albert Camus - but this is a good one.
And, seeing as how I was late with this one, here's another for free:
"Every existing thing is born without reason, prolongs itself out of weakness, and dies by chance."
That's much more like the jolly old Sartre I've come to know and avoid - what a happy thought at the start of the week...