It mentioned how every person (and especially us musically inclined 20 somethings) has a song that always cheers them up or makes them want to sing and dance along, almost every time they heard it.
Mine has been "Sofa Song" by The Kooks (for many years now).
"Scotty Doesn't Know" by Lustra - from the soundtrack of Eurotrip, "Want You Bad" by The Offspring, "Raise Your Glass" by Pink, "On the Radio" by Scouting for Girls and *hides with embarrassment* "Mmmbop" by Hanson.
"Sofa Song" has always been my "happy song", but I also have an additional 'new' one every month or week even:) Music is lovely that way...
Birdhouse in Your Soul - They Might Be Giants
You need to hear this one if you haven't. It poops all over your happy songs.