Patriot Games was really good.
Yes, I loved this one, also. Both book and movie - which we saw a couple of weeks ago for the umpteenth time.

My son graduated from USNA in Annapolis, and it was cool being able to picture the area while reading the book, and the scenes filmed there in the movie.

The scariest books were Sum of All Fears and the one where the 'ebola' gets released.
Speaking of ebola, have you ever read The Hot Zone by Richard Preston? That's a true story that will make you have nightmares.