I think with a special song, it's IMAGINE of John Lennon, it's a music for think about a society's dream. This song is very popular on the world for its letter and the meaning.
Anothers songs about happiness there are a lot of LluÃs Llach (Estaca, Laura, Dona'm la mà , Tinc un clavell,...) These songs are very special for catalan people that like this kind of songs.