It's the easy pick to make but Raining Blood. I just love the riff so much. I won't shy away from it just because it is the most well known and popular song from them.
To me their run from 85 to 90 is really good album wise from Hell Awaits, Reign in Blood, South of Heaven, and Seasons in the Abyss.
Though I'm not going to pretend I'm a massive Slayer fan. I knew them, I liked them, I listened to them occasionally but at the time I favored a lot of other groups over them.
PSN ID: sled_dogs76
60" Pioneer Kuro Elite PRO151FD, Yamaha RX-V3900 A/V Receiver, Oppo DV983-H player. Coming soon: 2 Seaton Submersives from Mark Seaton