Death Metal - Bands like Cryptopsy, Suffocation and Nile, low tuned, fast, alot of trem picking usually gory lyrics... but not always.
Black Metal - sucks... lol but its these goons that wear clown makeup, sing about hating jesus and burn churches.
Metalcore - Bands like Unearth and All That Remains, mostly melodic, probably my favorite type of metal.. of course if you think atreyu's metalcore then i can see why you wouldnt like it..
Thrash - Old Metallic, Slayer, Exodus... cmon everyone knows what Thrash metal is