Pick 5 from these
Sabbat - History Of A Time To Come (one of my top 5 Thrash albums ever... unique sound. Dreamweaver is also really good)
Voivod - Dimension Hatross (since they included prog influences on their sound these guys simply kill! Phobos and Killing Technology also rule)
Kreator - Hordes Of Chaos (No need for introductions.... these guys are a milestone in Thrash. Could have gone with early classics like Coma Of Souls or even Violent Revolution but there's something in this album that's simply relentless)
The Haunted - rEVOLVEr (This album DESTROYS! Period.)
Testament - Low (perhaps The New Order is their best album but there's something in Low that really sticks with me)
Overkill - Years Of Decay (Feel The Fire is amazing as well .. plus it's their debut)
Shrine - Perspective (great Prog Thrash from Portugal)
Xentrix - For Whose Advantage (Shattered Existence is also a great record)
Confessor - Condemned (another Prog Thrash gem)
P.S. I didn't include the following bands on this list because though they have Thrashy elements I don't think they fit the genre:
- Sepultura: even Schizophrenia and Beneath the remains have a lot of Death Metal in it. Chaos AD is a mix between Death Core (precursors to the genre) and groove metal. Then Roots to Nation their sound was full of crappy Nu Metal. My favorite Albums are (in this order) Chaos AD, Arise, The Mediator, Beneath The Remains, Kairos, Dante XXI and Schizophrenia.
- Pantera: Let's put it simple... this guys along with Exhorder invented Groove Metal. Power Metal is Speed/ heavy metal though. I don't count the pre Anselmo records. From Power Metal to Reinventing The Steel there isn't a single record I dislike.
- Celtic Frost: on can claim that their 2 first records are kinda tharshy but the sound is so "all over the place"... Thrash, Dark, Black metal: all those genres were influenced by these albums (and Gothic Metal with Into The Pandemonium). Nevertheless Vanity/Nemesis, Into The Pandemonium and the superb Monotheist are my personal favorites.
- DRI: Thrash zone could be included... but despite the title I think these guys sound is better defined along with Suicidal, SOD and Acid Reign in the Crossover section.