Today in Roger Ebert's blog, he perfectly describes that feeling. It happens to him in movies where someone does something right (as in Clint Eastwood's character's actions at the end of Million Dollar Baby.) These kinds of movies also make me cry, more consistently than "sad" movies do.
This feeling is called Elevation:
Elevation has always existed but has just moved out of the realm of philosophy and religion and been recognized as a distinct emotional state and a subject for psychological study. Psychology has long focused on what goes wrong, but in the past decade there has been an explosion of interest in "positive psychology"--what makes us feel good and why. University of Virginia moral psychologist Jonathan Haidt, who coined the term elevation, writes, "Powerful moments of elevation sometimes seem to push a mental 'reset button,' wiping out feelings of cynicism and replacing them with feelings of hope, love, and optimism, and a sense of moral inspiration."Now, I am not necessarily morally inspired by marching veterans, but I am inspired by the fact that they show up and let their physical bodies publicly stand for something they believe in. To me, that is a right thing.
Studies have indicated that Elevation is triggered by the stimulus of our vagus nerve, described by Wikipedia as the only nerve that starts in the brainstem and extends down below the head, to the neck, chest and abdomen, where it contributes to the innervation of the viscera. It must be involved in what we call "visceral feelings," defined as "relating to deep inward feelings rather than to the intellect."
I recommend reading the whole Ebert post, btw. He is my new favorite internet philosopher.