Popular songs about happiness:
Oh happy day (Edwin Hawkins, gospel song, http://www.youtube.com/watch?v=JQcQWpABjfw)
Don't worry, be happy (Bobby McFerrin, http://www.youtube.com/watch?v=PE9ZXh0Fuwk)
Beautiful day (U2, http://www.youtube.com/watch?v=u6FwEJwwYcQ)
Shiny happy people (REM, http://www.youtube.com/watch?v=RXywQQ4EX7U)