I know:
1. The Star-Spangled Banner: I'm an American...
2. O Canada: I live right next to Canada. I've been to NHL games. Etc, etc.
3. Bilady, Bilady, Bilady: This is the Egyptian national anthem, which I know because I'm of Egyptian origin (second generation, and I've been to Egypt). It's a simple song, too.
4. God Save the Queen: I learned this in school; the music teacher was British, and when we learned "America" (aka "My Country 'Tis of Thee"), she had us learn the original lyrics.
5. La Marseillaise: Learned it on a whim after reading a translation of the lyrics ("Let's march until impure blood drenches our furrows." Really?).
6. Deutschlandlied: A friend of mine is learning German, so we humorously sang this en route to campaign work...It was bizarre.
So 6. I also tried learning the Hymn of the Soviet Union (to go with my Nikita Khrushchev costume), but I failed.