When we are talking straight up Metal, then I am thinking Metallica, Pantera, Lamb of God, Avenged Sevenfold and Slayer.
Metallica is of course the best way to get into heavy metal, after that I began drifting into Green Day, Punk and Metalcore territories until I began rediscovering straight up heavy metal this year. Pantera made a god like genre that is fucking immortal and never gets old, and that's where Lamb of God comes from. Slayer is the other band in the Big 4 I like other than Metallica, the other half, Anthrax and Megadeath I have never been fond of. Avenged Sevenfold also came across early on, I like Hail to the King but the albums with the late Jimmy Sullivan like City of Evil, the Self Titled and Nightmare are definitely the superior A7X albums.
I definitely like a lot more than just that, stuff like Korn, Asking Alexandria, August Burns Red, Parkway Drive, and Of Mice & Men I consider Metal.
@Black Wizard Gojira is cool, I've given them a shot because of this thread.