Metallica-Master of Puppets (It's either this or Ride the Lightening, depending on which you hear first)
Anthrax-Vol 8
Pantera-The Great Southern Trendkill (their best album, period)
Slipknot-Vol 3
High On Fire-Blessed Black Wings
Pelican-The Fire In Our Throats Beckon The Thaw
Deftones-White Pony
That's probably where I'd start. People have listed some other excellent albums (Toxicicity, Jane Doe, Astro Creep, Peace Sells) and bands (Sabbath, Sabbath, Sabbath). I'd probably add Soundgarden, Neurosis, the Melvins, Isis and Zeppelin.
For pure hate, I doubt there's anything as nasty as Tool's Anema, except for Slayer's Disciple.
But for anyone into metal, if you have the time I say go back and listen to what's been done. There's some amazing stuff back there and you don't have to wade through the shit.
/not hatin' on the new stuff
//just don't want to see the history forgotten