Maté is the "official" drink of Argentina. My parents have been living there for a couple of years now, and have gotten used to the very bitter, gritty taste. It is served in little almost-teardrop-shaped cups called a cuia that are often very decorative and it is drunk through a unique little metal straw called a bombilla with a strainer built into the end that goes into the cup (to strain out the leaves, I assume). I didn't try it, myself (coffee is too bitter for me), I stuck to the "submarino" -- hot milk with a small bar of rich chocolate dropped into it to melt. Mmmmm.

EDIT: Here's a good site for more in depth info:
http://agronomy.ucdavis.edu/gepts/pb143/crop/mate/mate.htm