Oh gosh I love anthems, and have the lyrics to quite a few. I love singing along to them.
My favourites are Land of My Fathers, Flower of Scotland, God of Nations, Nkosi etc, Samoa Tulai, the Italian anthem, the Tongan anthem and now that I've heard it, the Argentinian one.
I also love La Marseillesaise, but have been surprised at how reserved the current French team are when singing it. Comparing the Argentinian singing to the French singing in the opening match, the French just didn't seem to be as moved when singing it as they used to be. Thought it didn't bode well for the French in the game.
When going to internationals I try to get tickets to the stand which faces the teams as they sing the anthems. It's just awesome!