I dont think Dead Snow gets alot of recognition, it's a good zombie flick.
Heartless, a brit-fantasy-horror from 2009 with Jim Sturgess is another I watched a couple of years ago on a whim and really dug. Not something I hear anyone discuss but I thought it was an interesting one.
The Legend Of Hell House. I was part of a "Best Haunting/Ghost Movies" discussion a few months back and this never got mentioned. One of my favourite horror films and definately one to see if you like ghost stories. Its from 1973 and is all about the atmosphere.
Session 9 and The Changeling are two other great ghost story/haunting films but I'm not sure if they're underrated or not because I know alot of people who love them.