I would say the most popular by far is West Side Story," made and set in the 60's. But there are a whole bunch, since it's a very common story.
There's also "Romeo Must Die," an R-rated martial arts film set in 2000's China, "Gnomeo and Juliet," which is more "modern day" and has a happy ending, since it's for kids, and "Warm Bodies," which is basically just Romeo and Juliet but modern day and he's a zombie.
