Not sure which one, but it’s definitely Sabbath. Probably “Black Sabbath” (the song) for me – never have three notes sounded so sinister and foreboding, but honourable mentions for Iron Man, War Pigs and Sweetleaf.
For those liking things a little less heavy, Brian May’s had a few, but rather than his better known ones, I’d go with “Son and Daughter” from Queen’s first, eponymous album.
Sunshine of You Love is a good one (Cream).
Beatles – Day Tripper?
Blur – Song 2?
That Kasabian one that the crowd sing back when they play it live (can’t remember the name, the one off the first album that goes “Boom! Na nah nah nan nah na-nah Boom! Nah nah nah na-nah na-nah”
Actually scratch all of the above because I’ve just remembered the riff to end all “which riff” arguments, as played by the largest assembly of A-list bass players (and some others) probably ever assembled:
[video]https://www.youtube.com/watch?v=iN42uzNFVmQ[/video]