Well, I like VGM a lot, and I frequently start singing some good songs. This are probably among the songs I like the best if I want to sing. They are not my favorite songs. They all belong to very good games.
Ridley's Hideout from Super Metroid: well, this is Wikitroid, you should know this song. It makes you feel that you're in hell (and you are). Definitely more fun to sing than Magmoor Caverns, which I think is better. http://www.youtube.com/watch?v=CdO8hH3BlJY
Flower Garden from Super Mario World 2: Yoshi's Island: it plays in what I call "rocky levels", such as Worlds 2 and 4. I like jumping around with Yoshi when I hear this song. This song appeared in Brawl, too, but it's not as cool as the original. http://www.youtube.com/watch?v=wJ_hUgYKiv0
Dark World from The Legend of Zelda: A Link to the Past: when you travel to the Dark World, an alternate version of Hyrule, you no longer get the classical Zelda theme, you get this one! It's had some remakes, but this one is the best. http://www.youtube.com/watch?v=H-kqzc4gcnw
So, please tell me your favorite three songs to sing. BTW, did you notice that the three games are for SNES? :P