My favorite longer-form motivational piece is the famous Henry Rollins one...been posted here before, will be posted again.
This one's taped on my mirror, pinned on the bulletin board by my desk at school, and often on my mind:
"The Iron is the best antidepressant I have ever found. There is no better way to fight weakness than with strength. Once the mind and body have been awakened to their true potential, it's impossible to turn back.
The Iron never lies to you. You can walk outside and listen to all kinds of talk, get told that you're a god or a total bastard. The Iron will always kick you the real deal. The Iron is the great reference point, the all-knowing perspective giver. Always there like a beacon in the pitch black. I have found the Iron to be my greatest friend. It never freaks out on me, never runs. Friends may come and go. But two hundred pounds is always two hundred pounds."