For good, accessible and melodic thrash like Metallica and Megadeth, check out Metal Church's first two albums, Annihilator's Alice in Hell, Forbidden's Twisted Into Form, Artillery's By Inheritance, and Realm's Endless War.
For something along the lines of Pantera, try Exhorder and Invocator's Weave the Apocalypse (think a technical/progressive Pantera).
For favorites of mine in general, Fates Warning is my favorite band (I love everything from their early Maiden-y stuff to their flashier progressive period to their more minimal and dark later stuff). Psychotic Waltz and Watchtower are also two of my favorites, also early progressive metal pioneers, the former with a bit of a psychedelic vibe and the latter on the hyper-technical side of things.
Fear of God's Within the Veil is a really good album and is worth hearing if you want something dark. The closest description I could give would be Alice in Chains playing Slayer riffs with rather harsh female vocals. Sort of a grungy thrash metal, but they pulled it off excellently.