RodneyP wrote:This little lot are more psychological...
OMG... this movie is seriously SOOOOOO MESSED UP!!!
Absolutely, without a doubt, the most disturbing movie I've ever seen in my entire life. And probably for the rest of it, too. I don't remember it being so much scary as much as it was disturbing. It's from Japan... and they know their horror pretty well. Dee mentioned "The Ring" which was a remake of the Japanese "Ringu"... both are a good, though "purists" would say the Japanese is scarier. I actually liked the English version better. If you like the Japanese style, there's "Ju-On" (The Grudge) and "Jissatsu Circle" (Suicide Club).
"Martyrs" (which YogurtStorm mentioned) is pretty disturbing as well.
Other notably faves in the genre I can think of right now are "Event Horizon" (being a fan of sci-fi horror), "Descent", and "The Blair Witch Project". If you like the documentary-style of Blair Witch, you could also check out "REC" or the US remake "Quarantine".
Less scary (but still enjoyable) movies I have in my collection (that I can remember off the top of my head) are: Cloverfield, 28 Days/Weeks Later, Dawn of the Dead (the remake), and The Shining (the original by Stanley Kubrik).