I went with English Lit/Writing, you've got to be able to put together a good story or it's just number crunching.  My wife's a mathmetician, and it is nice sometimes to have her around.   

I went with Art/Music and would have voted for Drama if it were offered.

Those disciplines are about Form, Structure and Emotional Resonance - communicating through sound and visuals for great impact on the observer/viewer/participant.

You think you have to "know" a thing or two to run a successful RPG, and IMHO, you have to know how to touch the player's imaginations and heart - otherwise it becomes dull and uninteresting.

Obviously, this IS multi-disciplinary in bringing an exciting experience to the table.

But I can quote facts, let scientific principles be understood from other media - yet when I have to RUN the game and get the PCs palms sweating or have a thrilling chase to catch a villain, I need to know how to embrace, cradle and magnify all their fears, hopes and weaknesses for gripping drama.

Art helps me do this. So does Music - simply by having to learn the power of tempo and rhythm.

The rest is good, but the question was "What class helps you the most in 'role-playing games'?

I would say anything increasing role-playing of the PCs by a bunch of bored gamers!

And when you start out a super-spy game with THIS, you can't keep them uninterested for long!