The squeaky wheel gets replaced.
Those who can, do; those who can’t leech.
I usually go with, “We’ll jump off that bridge when we get to it.” 
Another personal favourite - “That’s how the cookie bounces.”
My favorite is from Groucho: Time flies like an arrow, and fruit flies like a banana.
It’s all fun and eyes until someone loses a game.
It’s all fun and games until someone loses an eye - then it’s fun and games in the dark.
Even a stopped clock finds an acorn once in a while.
In the land of the blind, there is only one type of dating, and upturned rakes are particularly hazardous.
It’s not the heat; it’s the stupidity.
I pitied myself because I had no shoes, until I met a man who had no feet. So I took his shoes. (I can’t claim credit for this one, though I don’t remember where I heard it.)
An apple a day really doesn’t make that much difference in your overall health, unless you also cut out the junk food, quit eating so much cholesterol, and get some exercise for once, you fat pig.
A rolling stone gathers no moths.
Two roads diverged in a wood, and I–I took the one less traveled by. It made no difference whatsoever. I was still late. Traffic was terrible.
Good one.
Reminds me of my High School teacher. He wasn’t cut out for the career, and was spectacularly uncomfortable addressing a room full of teenagers. One morning he tried to relate the “no shoes” homily, and I’ll never forget his exact words:
(fidgeting nervously) “I felt sorry for myself because I didn’t have any shoes, but then I saw a guy walking down the street without any legs.” Hilarity ensued.
.
Outside of a dog, a book is a man’s best friend. Inside of a dog, it’s too dark to read.
Give a redneck a fish and he eats for a day. Teach a redneck to fish and he’ll bankrupt the family buying shit at the Bass Pro shop.
How about:
I cried because I had no shoes, until I met a man who had no feet. And then I laughed
(too dark?)
One that I had to amend only recently (which explains it’s unwieldiliness):
No-one can make you feel inferior without your consent. Of course, they’ll still think you’re inferior, and they can still exercise whatever imbalance of power over you that raised the issue in the first place, but by golly they can’t make you feel inferior.
A bird in the hand is gonna poop on you.
Time flies when you’re in a coma.
Give me immortality or give me death! (Firesign Theatre)
An old one: Smoke, and the world smokes with you; swear off, and you smoke alone.
A stopped clock is right 24 times per day, somewhere in the world.
A bird in the hand is always greener than the grass under the other guy’s bushes.
From one of the most subversive films of all time, North.
Idle devils make handy workers.
You’ve buttered your bread, now you can lie in it.
I think I’m in love with that one.
“A think worth doing is worth doing badly.” I believe this to be true for three reasons. In fact I have a seven minute speech about it. 
First graders are supposedly pretty good at this.
“If you lie down with dogs, you’ll stink in the morning.”
A straight line only exists to a first approximation.
A bird in the hand is either dead or dying.
The grass is always greener near improperly-stored explosives.