A co-worker of mine is looking for a horror-type book, but not necessarily the gross-out type. He wants one that's kind of freaky, weird, creepy - the kind that makes you want to toss the book across the room and have shivers up and down your spine. He said The Exorcist did that for him. Anyone have any recs for him?

IT by Stephen King scared me pretty good. Also The Shining.  Thinner was definitely the creepiest, as well as the shortest, of the three.

I'll try to think of another author.

Ok, Ice Limit and Relic by Douglas Preston and Lincoln Child were excellent.

Many thanks!

Heart Shaped Box by Joe Hill is excellent. 

I agree with above selections and would add an oldie by Peter Straub called Ghost Story.