For gym motivation:
"First, be a good animal." -- Ralph Waldo Emerson
"The whole duty of man may be expressed in one line--make yourself a perfect body." -- Henry David Thoreau
The entire poem, "I Sing the Body Electric" by Walt Whitman is inspiring in the gym! It's a loooong poem; this is the gist of it:
"If anything is sacred, the human body is sacred.
And the glory and sweat of a man is the token of manhood untainted,
And in man or woman a clean, strong, firm-fibred body, is more beautiful than the most beautiful poem....."
Also:
"A pint of sweat saves a quart of blood." -- General Patton
And this old classic works for me: "PAIN IS JUST WEAKNESS LEAVING THE BODY." Dunno who said it, but I know that EVERYBODY quotes it!