There's so many to pick that are epic but here's a few off the bat
Hell's Bells- AC/DC: The haunting Dennison Bell, and the opening guitar riff that hooks you right in
For Whom The Bell Tolls- Metallica: Very similar bell, yet not as pronounced. This time, it's the opening bass line that hooks you.
Time- Pink Floyd: The ticking of the clocks and heartbeat rhythm
The Hellion-Judas Priest: the whole riff opens Electric Eye and sounds like the very definition of metal
Aces High-Iron Maiden: the guitar rhythm sound like an air warning while the drums sound like artillery blasts. Compound the live versions with Churchill's speech and it's perfect.
Seasons of Wither-Aerosmith: there's a swirling wind sound (done by rocking a volume pedal back and forth) that is very cool, followed by a slowly increasing acoustic riff
War Pigs- Black Sabbath: the air raid sirens again, though this time they're real and the crushing riff that is pure doom
Money for Nothin'-Dire Straits: the drum beat over the synth noise, followed by one of the coolest guitar riffs ever recorded.
Bad Motor Scooter-Montrose: Ronnie Montrose got the best motorcycle sound gearing off out of a guitar
My Curse-Killswitch Engage: absolutely beautiful clean guitar open, followed by a equally beautiful distorted guitar harmonizing with it into a wicked full rhythm section backing it