I was never into death metal that much to be honest, but here's my take on the highlights of the genre:
Death (the band) - Scream Bloody Gore, Human, and Symbolic. The first one is really a death metal pioneer and one of the earliest examples of the genre in question together with Possessed - Seven Churches. Human has that classic Scott Burns Morrisound studios sound. One tip for anybody who wants to explore death metal is to check out everything recorded at Morrisound and produced by Scott Burns. Symbolic is more melodic and almost power metal influenced, but still sounds as a trademark Death record.
Morbid Angel - Particularly Altars of Madness and Formulas Fatal to the Flesh. Trey's guitar playing is wicked and this band produced perhaps the most interesting sounding death metal of the 90's.
Deicide - s/t and Once Upon The Cross. Very brutal and unique band, despite being quite simplistic in its expression.
Cannibal Corpse - Tomb of the Mutilated for ultra gory lyrics. Later material with Corpsegrinder as vocalist also cool, especially Bloodthirst and The Wretched Spawn.
Nile - Also a very unique band that takes inspiration from ancient Egypt. Check out In Ther Darkened Shrines or Annihilation of the Wicked. Brutal, fast, but still very catchy.
Suffocation - Effigy of the Forgotten. The beginning of "technical death metal" or even "slam".
Entombed - Left Hand Path: total classic from Sweden.
Bolt Thrower - The IVth Crusade: this band is like a panzer tank grinding everything in it's way very slowly and painfully.
Autopsy - Severed Survival. A bit like early Death but somehow more sleazy.
Some newer pretty interesting stuff includes Necros Christos - Triune Impurity Rites. Kind of "occult" death metal.