More than once, the eponymous protagonist of the Scott Pilgrim series has used the power of rock against his enemies, most notably at the ends of volumes one and three. Since he himself isn't that great a musician, usually other people are helping him out. And the music alone isn't enough to truly defeat the opponent, but it does weaken him sufficiently for Scott to take him out with some good old-fashioned fisticuffs.
Additionally, Matthew Patel could summon hordes of minion girls with his Bollywood-style fighting, and Crash and the Boys, rival group to Scott's band Sex Bob-Omb, can put audiences into a literal daze with their music.
The infamously deplored weekly series Countdown to Final Crisis had one good thing: when the Pied Piper (a Flash's ally) uses this to drive away Brother Eye/OMAC, the giant space entity. Not just the power of any old rock, either. Behold, the power of QUEEN!!.
Occasional X-Men member Dazzler's powers work by converting sound to light (which she can then use as laser beams). Naturally, she picked a musical career. Fighting evil with the power of... erm... Disco.
In The Power of Shazam! issue 18, Mr. Mind has just been made into the last surviving member of his species, and to exact his revenge on the Big Red Cheese, he possesses the Wizard, who, running away from Mr. Mind, had fled into a sound studio. Knowing the worm species has a weakness against loud sounds, Captain Marvel gives the Wizard a headset, picks up one of the electric guitars laying around, and starts to play like "Hendricks".
In Joss Whedon's one-shot comic Sugarshock!, a band mistakes an invitation to an alien tournament for a Battle of the Bands and proceeds to try to use the power of rock. Played with in that the band wins not through epic rock but with the saddest song in the world. One voice. One guitar. In-universe Tear Jerker. Only squirrels were unaffected because squirrels have no souls.
Image Comics' "The Amazing Joy Buzzards" is about a rock band and their luchadore friend who battle supernatural hipsters, demonic robots, and fallen angels.
Asterix and Obelix's village bard has made the Normans run away in fear and made it rain in an Indian draught.
Another X-Men example is more obscure New X-Men member DJ aka Mark Sheppard who, before being depowered after House of M, is granted different powers depending on the music he hears. Some is more utilitarian: Light manipulation when he hears dance music, flight when listening to uplifting Gospel music, while classical music allows him to generate energy shields. However the literal Power of Rock is energy blasts.
The DC Comics mini-series Sonic Disruptors (published 1987-88) was created and written by Mike Baron and illustrated by Barry Crain. It was arguably the apex of this trope. The United States has been taken over by an evil militaristic government that hates fun and has banned all rock music, among other fun things. The resistance movement is rock-based, flies guitar-shaped fighter jets, and broadcasts illicit rock music into the U.S. from their secret space station. The series was cancelled seven issues in to its planned 12-issue run.
Going back to the same premise many years later, Mike Baron collaborated with illustrator Gabe Eltaeb on the webcomic and graphic novel The Hook subtitled "Sci-Fi Rock". It was, for all practical purposes, Sonic Disruptors transplanted to an intergalactic setting.
Subverted horribly in a National Lampoon parody of Yellow Submarine that chronicled the downside of The Beatles' career - as in the movie, they attempt to rout the forces of evil with a song about love - and crank out 'Helter Skelter"...Paul later comments "That didn't quite work out like we'd planned..."
Played with in Astro City with Sticks, a talking gorilla from a militaristic gorilla society who left his home to pursue a career as a rock drummer. Due to his superior strength and agility, both heroes and villains from Astro City wanted to recruit him, making his efforts to simply be a musician difficult. Ultimately he became a hero, working alongside some of Astro City's more recognized heroes until he announced to the press that he was auditioning other music-themed heroes to start their own super-team/rock band. As of the end of his introduction the new team was voting on a new name. Sticks was partial to "Powerchord."
Astro City has had a number of heroes and heroines, dating from its foundation as Romeyn Falls, who carried a strong musical influence, usually with powers associated with the popular music of the times. Among the more prominent were Silverstring (a demon slaying troubadour from the 1870s), Mister Cakewalk (a Ragtime-inspired vigilante from the 1900s), Jazzbaby (a jazz-themed heroine from the '20s), Zoot Suit ('40s big band), the Bouncing Beatnik ('50s hep cat), Halcyon Hippie ('60s psychedelic rock), then finally Glamorax (David Bowie-inspired glam rock of the '70s).