By which I mean: not "My favourite band's song which has a riff that I happen to really like", but Bands that crank out killer riffs as their basic stock in trade.
AC/DC are probably the glaring mainstream choice, but I was listening to Brainbombs yesterday and thinking that those guys are honestly up there with The Stooges when it comes to all-time classic crushing caveman riffs, played with just the right mix of loose, scuzzy flailing & lethal precision. It's hard to come up with a great simple riff, and even harder to nail it just right.
So: Brainbombs. Also, Frank Black. Nobody ever talks about his riffs, but he's got dozens of absolute blinders scattered throughout his & the Pixies' canon.
Tell me about more great riff-meisters and I'll check them out.