I thought Saw was a great idea which they could have done better with, I enjoyed it but the twist rather spoilt it for me as it became rather implausible. Still, it is worth a viewing

. - a similar concept to 'Cube'
I think there are 3 types of scares, :-
the spooky ones where you see what is happening and it is rather un-nerving (the twins in The Shining) >

the uncomfortable ones which usually involve pain or gore (Leatherface hitting someone with a lump hammer, someone in sheer panic as they realise they are trapped in a nasty situation. :G)
The suspense - these usually set the scene, and can be very creepy if watched under the right conditions.
Often a suspense scene is followed by what I dont consider to be a genuine scare - a 'jump'. - I didn't find the Descent scary.
I've already mentioned 'Ju-On:The Grudge' (in a previous thread), which I watched last night in a darkened room listening via headphones, I found that to be very creepy.
I also rate :-
The Shining,
The Exorcist,
Texas Chainsaw Massacre
The Thing (just pure paranoia and suspense, anything goes).
and who can forget the kid floating up to the window and tapping on the glass in 'Salems Lot'