If you can handle subtitles check out Infernal Affairs, the film The Departed is based on.
I hadn't realised it was a remake until I was watching it at the cinema. It was shortly after watching Internal Affairs and I was surprised how strikingly alike the two films are. Happens too often these days, no need for remakes when the originals are still perfectly good.
I'd still recommend watching either though, great story and both adaptations good.