All Star, by Smash Mouth, that one off of Shrek.
Eye of the Tiger.
Simply the Best.
Always look on the bright side of life
That one with the sunscreen.
Basically anything upbeat that either tells you things are gonna be all right, or something upbeat that contains a lot of rapid distracting images like "Cool for Cats". Reminds you of how there's more to life than just grades and getting locked into the machine. This applies to both those with low grdes as well as those with high ones, who'd often do well do get down off their high horses.