A few that I have been influenced by over the years:

People will believe anything you say if you tell them that Benjamin Franklin said it first.

Never attribute to malice anything that is more easily explained by stupidity.

99% of all human wisdom consists of a willingness to keep your mouth shut. – Albert Einstein

You are entitled to your own opinion. You are not entitled to your own facts. – Carl Sagan

Don't let yesterday use up too much of today.

Opportunity is missed by most people because it arrives in overalls and looks like work. – Thomas Edison

When you are going through Hell, keep going. – Winston Churchill

All generalizations are false, including this one. – Otto Koppen

Pick your battles big enough to matter, small enough to win. – Jonathan Kozol

There is always an easy solution to every human problem–neat, plausible and wrong. – H. L. Mencken

Panic is what happens when you run out of training. – Sandy Stevens

With all your getting, get understanding. – Proverbs 4:7