i'd recommend gummo, i think. it's... not that great a film, but it's worth seeing. i don't know. it's a lot to bear, emotionally and spiritually (and even physically; you'll know what i mean when the bathroom scene happens). it's also probably the most masturbatory film ever created, and probably isn't nearly as aesthetically meritorious as korine thinks it is.
that said, it has one of the most beautiful and heart-wrenching endings of any movie i've ever seen, so it's worth sticking through it until the end.