Let the Right One In is a Swedish horror film directed by Tomas Alfredson. It is based on the novel of the same name by John Ajvide Lindqvist, who also wrote the screenplay for the film. It tells the story of a bullied 12-year-old boy who develops a friendship with a vampire child in Blackeberg, a suburb of Stockholm, in the early 1980s. - Wikipedia
I just watched this, and I was so impressed that I went and ordered the book because apparently that has even more backstory about Eli and how she came to be a vampire. I recommend you guys check this film out, it's what Twilight should have been. Here's a link to the PirateBay torrent, so no excuses to not watch it now.