I rotate em in my sig a bit; My personal favorites are:

You see things; and you say, 'Why?' But I dream things that never were; and I say, "Why not?"
George Bernard Shaw

The income tax has made more liars out of the American people than golf has.
Will Rogers

Bigamy is having one wife too many. Monogamy is the same.
Oscar Wilde

The hotter the forge, the stronger the iron
Bipper

Stand tall in your convictions like a Seaside cliff; Because crumbling will make you a beach.
Bipper

Of all the animals, man is the only one that lies.
Mark Twain

Capital punishment is as fundamentally wrong as a cure for crime as charity is wrong as a cure for poverty.
Henry Ford

I am enough of an artist to draw freely upon my imagination. Imagination is more important than knowledge. Knowledge is limited. Imagination encircles the world.
Albert Einstein

Capitalism is the astounding belief that the most wickedest of men will do the most wickedest of things for the greatest good of everyone.
John Maynard Keynes

Those are all pretty much my favorites