The unabridged The Stand got me into King, that was a ~700 page book that when I wasn't reading it, I was thinking about it. That doesn't happen too often, and it was unexpected as I was just looking for something long to read while stuck at an airport.
I really liked the first few books of the Dark Tower, but for some reason I lost interest and never finished Wolves of the Calla. I'll pick it up again someday, probably start at the beginning again as The Gunslinger remains one of my all-time favorites.
The last book that I couldn't put down was The Road by McCarthy. Looking forward to 11/22/63 quite a bit.
That's funny, "The Stand" (read the abridged version first and the unabridged version much later) got me into Stephen King as well. I was into the "Dark Tower" series when it first came out, but there was too much time between books to keep me engaged in the continuing story. I may have to give it a shot again in the future, but at the moment, I have too many books to read on the pile...