I just recently read Atlas Shrugged(I'm a late bloomer) and would put it in the "Must Read" category.
I thoroughly enjoyed "The Brotherhood of War" series from W. E. B. Griffin.
Anything and Everything by Robert Anson Heinlein, my favorite being "Friday"
I am about 3/4 of the way through "Point of Impact" by Stephen Hunter and have to say that I will be reading all of his books in the near future.
I was surprised at how good a read "Michael Vey: The Prisoner of Cell 25" by Richard Paul Evans was. It is juvenile fiction(as are more than a few of R.A.H.'s best stories) but very well written and a great story.
I also liked the "Rogue Warrior" books from Richard(Dick) Marcinko.
Alan Dean Foster
Phillip K. Dick
I could go on but...