I'm guessing as to which humanities courses would offer the best chances for doing well on the writing samples and verbal?
Take humanity classes that have NOTHING to do with science! Expand your mind (do I sound like a pothead saying that)?
HISTORY - Perhaps the most useful in my opinion of ANY class to take. As they say, history repeats itself and those who don't learn from it are doomed to repeat it.
ECONOMICS - Because so much of the world revolves around it, odds are you might get asked something about it or have a passage relating to world economics.
Anthropology/Ethnic Studies/Social Studies - Good idea just to learn how to look at other cultures and your own as well from different perspectives.
ENGLISH - Creative Writing, Poetry, Classic Studies.. you bet your butt there will probably be several chances to show off the knowledge you get from these classes!!
Art - Well, just personally because I know nothing about it and those questions always throw me for a curve ball and for some reason girls are really impressed when you take them to an Art museum.
Philosophy - Good to know, how to pose interesting questions or answer them in a way that you hope the Board is smoking out too as they grade your paper. Also, the various -isms would make for great passages to confuse the average MCAT taker.
Psych Classes - Do you guys count these as humanities too? Well, honestly.. a lot of it is common sense.. just relating everything back to wants and needs and lots of sex thrown in there too. Arguably you can claim society is merely an overblown courting ritual so people can get laid. But still, a great way to stand a question on its head, especially in essays.
Hope these help.