This is a (growing) list of films about the people who find out their neighbors are not quite who they claim to be. Can you think of any other titles that fit?
I've always seen this as an updated version of 'Rear Window'. We've got a kid on house arrest instead of a man in a wheelchair, but the rest pretty much lines up. see more on Disturbia
What if your neighbor turned out to be a blood-sucking fiend and no one believed you? This tale explores just that. see more on Fright Night
The current remake of ^the above title. I haven't seen it yet, but it looks to be about the same story.