The best I have seen in the last ten years is 'Hidden'.
It's in French, but don't let that put you off.
Another is the original verstion of '13 Tzameti'. Don't bother with the Hollywood remake, they toned it down for the US market. Don't read any reviews or even look on the box, it will be a huge spoil.. The less you know the better.
What an third? I quite like 'Timecrimes'. Another foreign language one, but you miss out a lot if you refuse for that reason.