Leaving out the really obvious stuff (Testament, Overkill, the Big Four, the Holy Trinity), here's a list of albums anyone who digs thrash outghta check out.
Sabbat (UK)- History of A Time To Come (awesome Destruction-esque thrash with a bit of a Celtic tinge in tone, with Martin Walkyier pre-Skyclad on vox. Amazing lyrics.)
Sabbat (UK) - Dreamweaver (more of the same–a bit more intricate and less balls-out thrashy than the last.)
Dark Angel - Darkness Descends (Just mentioning this in case some poor fool doesn't already own it. This album is to Slayer what Slayer was to thrash in 1986. Fucking UNHOLY.)
Morbid Saint - Spectrum of Death (Neckbreaking madness, like Dark Angel meets early Sepultura and then doubles the number of riffs. "Assassin" will damage your spine.)
Bifrost - The Wildest Fire (Similar to Sabbat, but a bit more dynamic and with a pagan Viking kind of tinge to it. Great stuff.)
Imagika - Devils On Both Sides (Power/thrash from SF veterans, kinda reminiscient of Forbidden but more melodic. Great live act.)
Deströyer 666 - Cold Steel...For An Iron Age (Phoenix Rising is their best album, but Cold Steel is the thrashiest. Pretty much everything by D666
rules, though–awesome, awesome black-thrash.)
Ulysses Siren - Above the Ashes (ZOMGWTFBESTOBSCURETHRASHEVER. Seriously, this seven-song comp of demo tracks shits all over 90% of the thrash metal genre–a lot of Exodus, a chunk of Heathen, some Coroner-esque time changes, and the occasional melodic salute to Iron Fucking Maiden. Beautiful. Just beautiful.)
Heathen - anything and everything (Speed/thrash wreckage. They rule. Enough said.)
Xentrix - Shattered Existence (One of the few really good third-wave thrash bands, hailing from the UK and kicking ass all over the place. Very classic Metallica/Megadeth kinda sound, with hints of the Nuclear Assault punk style.)
Andralls - Force Against Mind (Every Brazillian thrash band gets compared to glory-era Sepultura, but these guys are really the heirs to the throne. Very good new band.)
Torture Squad - Pandemonium (Absolutely fucking BRUTAL death/thrash, the kind of thing that will give you severe collarbone problems from trying to headbang to it. One of the best metal albums of the past five years.)
Dekapitator - We Will Destroy...You Will Obey! (A side project of Exhumed members that beats the fuck out of their real band–a rollicking, drunken tribute to the thrash metal of yesteryear that is all the better because it's obvious how much fun the band is having. One of those albums where the vocalist snarls "THRASH!" before every riff break. Glorious.)
Toxic Holocaust - Evil Never Dies (A one-man thrash project, notable less for riff complexity and more for beating your fucking skull in. Opening song "War Is Hell" is one of the all-time great thrash anthems.)
Vio-Lence - Eternal Nightmare (If you say you like old-school thrash and you don't own this, you are a poseur. It's been re-released. No excuses.)
Carnivore - Carnivore (Peter Steele's old band, before he decided he'd rather play shitty music and get laid. Gleefully offensive, hardcore-tinged NY thrash with awesome songs like "Thermonuclear Warrior," "World Wars III and IV," and the immortal "Male Supremacy."
That oughta do it for now.