An impossible question lol. Every one listed thus far can be argued.
A few that get regular rotation by me
Wish You Were Here - Pink Floyd
Whole Lotta Love - Led Zeppelin
Here Comes The Sun - Beatles
Sympathy For The Devil - Rolling Stones
Voodoo Chile - Jimi Hendrix
Drain You - Nirvana
No Excuses - Alice In Chains
Go Your Own Way - Fleetwood Mac
In Memory of Elizabeth Reed - Allman Brothers Band
46 and 2 - Tool
Wherever I May Roam - Metallica
Johnny B. Goode - Chuck Berry
House Of The Rising Sun - Animals (it's a cover but holy smokes it's timeless)
Smoke On The Water - Deep Purple
War Pigs - Black Sabbath
Tomorrow I'd have a slightly different list but most of these would still be there.
Edit: here's the live version of Elizabeth Reed from Fillmore East. Part of the finest live album ever IMO, and if I'm pressed it's either this or Here Comes The Sun.
In Memory Of Elizabeth Reed -Allman Brothers Band