Any distinctly British film, specifically Guy Ritchie's work, and films with Simon Pegg and Nick Frost in, redone by Americans. You guys have ruined enough of our TV series already, and we never do the same to your greats, so if you dare tarnish the bastion of awesome that is Hot Fuzz, I will personally declare war.
Other films: Inception, The Usual Suspects, The Matrix Trilogy, and some others I really can't be fucked to name.. they've already been said anyhoo.
In a relatively linked topic I really wish the Harry Potter films had been done with an extended version a la Lord Of The Rings, as the films miss out so much awesome that the books cover in detail. Quidditch World Cup, anyone?