1408 & The Shawshank Redemption - both the story and movie are pretty faithful adaptions from what I remember. 1408 was just ok and Shawshank was great.
Never read The Mist, but I really liked the movie. Which reminds me that I still need to watch the black & white version.
I just finished (500) Days of Summer. Really good movie about relationships that doesn't fall into the typical pitfalls. Joseph Gordon-Levitt is quickly becoming of my favorite actors.