I'll throw in Ihsahn (with strenght i burn anyone?, all of prometheus), Aaron Stainthorpe, MJK of tool, evoken, disembowelment, morgion (nighfall infernal, serpentine scrolls, a slow succumbing), that is what is coming off the tip of tongue (fingers) at the moment.
Karl Sanders, Oystein G. Brun, whoever write lyrics for Winds (Lars or Andy, I would assume), and some more, but those are my favorite metal lyric writers. I have other favs. in other genres.
-Iced Earth lyrics are always good, they've inspired a few of the poems I've written.
-Dream Theater, I love their music AND lyrics.
-Opeth, for obvious reasons.
-Iron Maiden, one of the only bands whose songs have made me cry.