There are so many good ones out there, but here are some of my favorites. Some are funny, some are profound, some are original. Some are even more than one, at the same time. More on the way!

"Everything in excess! Moderation is for monks and old ladies. To taste the spice of life, take big bites." <- This may be my all-time favorite, I love it.

"I always knew I would see the first man on the moon. I never dreamed I would see the last." --Jerry Pournelle

"Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover." - Mark Twain

"'Funny' is when you get hit in the head with a rock, and I don't!" - Charles Schulz

"If you have an apple and I have an apple and we exchange apples then you and I will still each have one apple. But if you have an idea and I have an idea and we exchange these ideas, then each of us will have two ideas." - George Bernard Shaw

"A government which robs Peter to pay Paul can always depend on the support of Paul" - George Bernard Shaw

"How far you go in life depends on your being tender with the young, compassionate with the aged, sypathethic with the striving, and tolerant of the weak and the strong. Because someday in life you will have been all of those." - George Washington Carver

"The lyfe so short, the craft so long to lyrne" - (Chaucer?)

"Too much of a good thing can be wonderful!" - Mae West

"An ignorant person is one who doesn't know what you have just found out." - Will Rogers

"Democracy must be something more than two wolves and a sheep voting on what to have for dinner" - James Bovard

"People who want to tell you about their religion very seldom want you to tell them about yours" - Dave Barry

"Against ignorance the gods themselves struggle in vain." -Nietzsche

"Peace is not the absence of war, but the universal presence of justice"

"All I ask is the chance to prove that money can't make me happy." - Spike Milligan.

"By the time you're 50, you have the face that you deserve."

"The world today [1988] spends $1 trillion [USD] a year on military preparations... That trillion dollars a year takes food from the mouths of poor people. It cripples potentially effective economies. It is a scandalous waste, and we should not countenance it." - Carl Sagan (*)

"A lot of people miss opportunity because it comes dressed in overalls and looks like work" - Thomas Edison

"Experience is a wonderful teacher, but only a fool will learn from no other"

"Don't cry because it's over, smile because it happened"

"Reality is that which, when you choose not to believe in it, doesn't go away." Phillip K. Dick

"I spent over 90% of my money on gambling, women and drink. The rest I wasted." - George Best

"The trouble with doing something right the first time is that no one appreciates how difficult it was." This is a .sig I saw once, somewhere. I might add: "so I hear".

"The power of accurate observation is commonly called 'cynicism' by those who haven't got it" - George Bernard Shaw

"There is no way to peace. Peace is the way." - A. J. Muste

"Before you criticize someone, walk a mile in his shoes. That way, if he gets angry, he'll be a mile away - and barefoot." - Jack Handy

"The early worm gets the bird"

"Direct experience is best. The man who carries a cat home by the tail gains information that will be useful all his life and will not grow dim in his memory." - Mark Twain

"I'm often wrong, but never in doubt"

"Doing nothing is only fun when you don't have nothing to do" - Jerome K. Jerome

"The speed of time is one second per second" <- This is from a student's physics lab notebook while I was a grad student in Physics. I have also used this as a sig file occasionally.

"Only the universe and human stupidity are infinite, and I'm not positive about the former" - attributed to Albert Einstein

"The first sign of the demise of a civilization is the callous disregard for effective and proper use of the prevailing language." - T. Lucas

"When you come to a fork in the road, take it!" - Yogi Berra

"I got a postcard in the mail the other day, from Ed McMahon! It said 'You may already be a loser'" Rodney Dangerfield

"I feel that if a person has trouble communicating, the very least he can do is to shut up." - Tom Lehrer

"Better to light a single candle than curse the darkness." - (Robert Browning?)

"You can't have everything - where would you put it?" - Steven Wright

"You can lead a horse's ass to knowledge, but you can't make him think" - [this might belong to Bob Silverman, I got it from his .sig]

"Good health is merely the slowest possible rate at which one can die"

The following quotes might actually be original. Then again, I might have just forgotten the origin:

"Opportunities to be a first-hand witness to poetic justice are so rare, they should be individually savored and treasured."

"Hindsight is always 50-50"

"The hallmark of a truly great idea is that it is obvious in retrospect"

"If that animal is so smart, what's it doing on my plate?"

"The reward for punctuality is patience"

"The two most dangerous drugs in the world are testosterone and stupidity."

"Never use an outhouse toilet while holding your car keys in your mouth" << This one is definitely original, a sometime sig file of mine. I'm speaking from personal experience here!

"If God wanted you to think, he'd have given you a brain"

"Rome didn't burn in a day."

"When God closes a door, sometimes He really nails that sucker shut."

(*): Sagan definitely said this, in his book Billions and Billions. But he was possibly inspired by Eisenhower:

"Every gun that it made, every warship launched, every rocket fired
signifies, in the final sense, a theft from those who hunger and are
not fed, those who are cold and are not clothed. This world in arms
is not spending money alone. It is spending the sweat of its laborers,
the genius of its scientists, the hopes of its children."