Madonnas cover of American Pie.
Britney Spears cover of I love Rock and Roll.
Atomic Kitten destroying Blondies Tide is High.
No Doubts cover of It's my Life
I also hate the recent trend of taking my favourite classic 80's pop hits and turning them into some cheesy euro pop...Infernal destroying Laura Branigans Self Control and some other crap murdering Hall & Oates Out of Touch.
I have loads more I loathe but these ones are just off the top of my head.