“I’ve done all that I can do, and that’s all that I can do.”
Keeps me from getting too stressed out when a situation goes out of my hands- also helps me to remember to try every channel before turning something over to someone else.
Or in the immortal words of the Sailorman:
"I yam what I yam and tha’s all what I yam." – Popeye
My favorite of late is “Resentment is like taking poison and expecting the other person to die.” It has really helped me get past some shit about which I was stewing endlessly.
The problem with the rat race is, even if you win, you’re still a rat. 
Working in IT, I find this one particularly apt:
“Some days the magic works. Some days it doesn’t”
Great! So instead of being paralyzed with fear, you’re distracted by reciting bad poetry. Either way, your opponent can disembowel you at his leisure…
Believing is Seeing.
That is brilliant.
"Always be excellent to each other."
—Bill and Ted’s Excellent Adventure
My words to live by.
**Time flies like an arrow…
Fruit flies like a banana**
Also – ASAP means “As Soon As Possible” – but no sooner.
And as a programmer, for me it’s “May the Source be with you!” 
Experience is what you have right after you need it.
Once a year go someplace you’ve never been before. - The Dalai Lama
“Surround youself with the kind of people you want to be like.” - One of my best friends.
Just because you’re paranoid doesn’t mean they’re not out to get you.
Try to be the kind of person your dog thinks you are.
I once got to (help) pilot an expensive sailboat. The owner said to me:
If you have to run aground, it’s best to do it slowly.
I find I can appropriate the sentiment into most facets of my life, with the possible exception of high explosives.
That’s a good one. It’s like something I read a while ago, talking about perspective and perception - you can be late and upset, or you can just be late. That applies to a lot of things that you don’t have a lot of control over.
Groucho Marx, right? I have always loved the clever symmetry of that.
One of my favourite sayings (along with “just because you can doesn’t mean you should”) is better to have it and not need it than need it and not have it.
What is best in life?
To crush your enemies, see them driven before you, and hear the lamentations of their womenfolk.
“Do what you want to do, and be nice to other people.”
Pain is your friend, it lets you know you’re alive.
(from some war movie)