Anything Final Fantasy.
The boss combat from number ff6, the boss music from ff7, the normal combat from ff7, Jenova's combat music from FF7, Cid's theme from ff7 as well, and of course, Yuffie's happy little tune. I'm always humming that one as I bounce down the side walk. Yes, I'm disturbed and damn proud of it.
And the Chocobo music. I wonder if there is a CD you can buy with every single Chocobo song on it. Now that would be money well spent.
And, of course, the greatest song ever from the greatest game ever...
THE BUBBLE BOBBLE SONG! That was an incredibly repetitive song that never made me bored to listen to it. Plus it had the most evil main character. Come on, those little dragons trap you in bubbles, kill you by touching said bubbles, then consume your soul which as just turned into a food product. Evil, I tell you, I love 'em so.