Eeesh, how can you pick just one? There are so many amazing first tracks... Well, ya'll know me to know I can't pick just one, so here's a 'short' list off the top of my head:
AC/DC - Hells Bells
AC/DC - For Those About To Rock (We Salute You)
AC/DC - Dirty Deeds Done Dirt Cheap
KISS - Detroit Rock City
KISS - Strutter
KISS - I Stole Your Love
KISS - Unholy
Paul Stanley - Tonight You Belong To Me
Dokken - Unchain The Night
Lynch Mob - Wicked Sensation
Motley Crue - Live Wire
Beatles - Come Together
Beatles - Sgt Pepper's LHCB
Scorpions - Blackout
Scorpions - Bad Boys Running Wild
Black Sabbath - War Pigs
Black Sabbath - Sweet Leaf
Black Sabbath - Sabbath Bloody Sabbath
Dio - We Rock
Triumph - Spellbound
Triumph - Tears in the Rain
Led Zeppelin - Whole Lotta Love
Led Zeppelin - Immigrant Song
Rush - Tom Sawyer
ZZ Top - Waiting For The Bus / Jesus Just Left Chicago
ZZ Top - Tube Snake Boogie
So much for a short list, eh?