Portugal: Grândola, Vila Morena - Zeca Afonso. Probably not a hit when it came out, as it was banned by the dictatorial regime at the time but it became the anthem of our 1974 revolution, pretty much because it was the song that the revolutionary group chose to be played on the radio station (they took control of) to mobilize their forces.
Zeca Afonso has a bunch of other well-known (and really good) songs, all sung in Portuguese but this is the one most people know by heart. It helps that it gets played every year on the anniversary of the revolution and whenever there's a protest.
Grândola is a good choice, though because of the political association it will never be a hit with the non-leftist crowd. Dunas or A minha casinha are probably more popular/neutral choices and, unlike Zeca's song, no-one outside of Portugal has ever heard about them (Grândola is well-known amongst at least some niche circles in Spain, where it was first released/sung during the dictatorship).
OTOH I'm fairly sure that in 50 years few will remember Xutos and GNR, while Grândola will still be sung over the centennial celebrations (assuming we don't fall back into a far-right dictatorship by then...)