Yeah, Slayer's kinda hit and miss with me. And Master of Puppets is my favorite album of all time.
The most pure thrash album IMO is Kill Em All, so you should check that out. Metallica's first 4 albums are all great thrash albums.
Other bands/albums I'd recommend:
Overkill - Horrorscope
Megadeth - Rust in Peace and Countown to Extinction
Kreator - Enemy of God
Metal Church - self titled
Exodus - Fabulous Disaster
Bonded by Blood - Feed the Beast
Hexen - State of Insurgency