Warning: songs are not guaranteed to be non-explicit. (In fact, they probably aren't.)
5. "Granger Danger"
4. "Ginny's Song"
3. "Not Alone"
2. "Different As Can Be"
1. "I Gotta Get Back To Hogwarts"
I literally reference this song in my everyday life. Whenever I pick up Harry Potter and the Philosopher's - I mean Sorcerer's - Stone, this song starts playing in my mind right after I get done with Hedwig's Theme. This song was what got me into these musicals, so I offer a multitude of thanks toward it - almost as many thanks as the words "Mr. and Mrs. Dursley of number four, Privet Drive, were proud to say that they were perfectly normal, thank you very much." These two things actually have something in common: I laughed when I saw it. (Nine-year-old me was very appreciative of the "thank you very much.")
Honorable Mentions
"To Dance Again"