There are a lot of great responses here, but surprisingly not much humor. Extreme amusement is an emotion right? Plenty of songs made me laugh really hard in video games, yes Still Alive was genius for multiple reasons, but from a pure empty laugh standpoint, these 2 were big for me:
From Conker's Bad Fur Day: http://www.youtube.com/watch?v=0w5neFPat1w
From True Crime Streets of LA: http://www.youtube.com/watch?v=PRjY-WIWV34
The Great Mighty Poo song was a very creative idea lol, and it was hilarious at the time.
As for the "***** Ass N****" song, I remember getting in a car in that game and hearing this song and thinking that it was a joke haha, i was crying with laughter. "And YOOOU look like, a ***** Ass Nigga (nigga!)"