I'll have to second Donkey Kong Country. Well, DKC2 more than the first one, but still. Lockjaw's Locker FTW. And the melody in the honey levels.
Of course, Super Mario World is easy, as it's 2 and a half melodies in 38 variations
The oddest one for me would be Final Fantasy. I have like half the soundtracks, but never actually played any of the games, apart from 2 hours of VI. I hate the battle system.