Great recommendation from Mitch (go figure), and a good flick.
Plot line - Shia LeBouf (great young actor) is an 18 year old kid put on house arrest for the summer. His mom takes away his XBox and iTunes, and he starts to get cabin fever ... and begins spying on all the neighbors. He soon realizes he has a serial killer living next door to him.
The twists and turns are a little predictable, but the movie keeps you on the edge of your seat and is well worth seeing. The acting of LeBouf, and female lead Sarah Roemer is very good IMO. And Roemer is drop dead gorgeous, and a star in the making. She had a bit part in Grudge 2, a significant part in this film, and the lead in a thriller called "Asylum" that is still in production.
IMO, she will be headlining films within a couple years, and like the girl from "The Departed", I had never heard of her ... yet came away jonsin to see her in more films. Some pics from the film are below.