Originally Posted by Pryda

Martyrs is just awesome, one of the best horror movies I've ever seen. I'm pretty sure you'll never forget it.

If you like it, check out these great french horror movies as well:
Frontiers <- my #2 after Martyrs
Inside (À l?intérieur) <- had to watch it in 2 sessions because I felt too uncomfortable, which rarely happens
Them (Ils)
High Tension (Haute Tension)

Interesting article about these french horror movies: http://en.wikipedia.org/wiki/New_French_Extremity