A stout is defined by it's ingredients. It's technically still and "ale" as it's often fermented with ale yeast but the grain that's used is often heavily roasted thus giving it the very dark color and rich flavor. a Porter beer would also be defined in the same way as it's named for the ingredients it's brewed with.
Other types of beer include (but by no mean limited to) Sours and Lambics.
Lambics are brewed with an open vessel in hopes of getting wild yeast from the air to ferment the beer.
South are very dark, rich, and filled with bitterness balanced by sweetness.