My Top Ten, in no particular order:
Shogun, James Clavell. He was a master storyteller. Set in the Orient around 1600, it chronicles the intrigue, manipulation, and double and triple dealing in the various courts of the warlords who, emperor notwithstanding, really controlled feudal Japan.
Knight's Cross, Sir David Fraser. If you are into military history or WWII at all, this biography of German Field Marshal Erwin Rommel will be a very satisfying read.
The Bourne Identity, Robert Ludlum. Arguably his best work. A deep cover operative loses his memory and tries to discover his true self while running for his life. Read it and understand why Richard Chamberlain and Jaclyn Smith were perfectly cast for their respective roles.
East of Eden, John Steinbeck. Without question the single most powerful ending of any book I've ever read. And I've been reading books for fifty years.
Watership Down, Richard Adams. A fascinating study of the power of believing in oneself in the face of overwhelming odds.
A Time To Kill, John Grisham. A riveting, ultimately accurate depiction of a racially charged murder trial in the deep south.
Lucifer's Hammer, Larry Niven and Jerry Pournelle. The disaster novel to end all disaster novels. A believable scenario that was clearly thoroughly researched, well-developed characters that you actually care about, and a storyline that will make you want to read in the car at red lights. Never again will you gaze at the stars without thinking of this book.
Dune, Frank Herbert. One critic is famously quoted on the paperback: "A triumph of imagination." Brilliantly conceived and flawlessly executed, Herbert creates an entire world with its own unique ecosystem, all the while showing the reader why love, loyalty, and honor will trump hatred, deceit, and betrayal every time.
Without Remorse, Tom Clancy. Actually, nearly every one of Clancy's Jack Ryan books could be on this list, but for my money this prequel, explaining how CIA superagent John Clark got to be John Clark, is the best place to start.
Sherwood, Parke Godwin. A study of the mythical rogue Robin Hood, and what his tale would likely had been if he really had existed. Godwin makes the Sheriff of Nottingham a tragic, sympathetic figure, vying for the affections of the Lady Marian with the heroic main character. Well written and historically accurate, it will forever change your thinking about the man who became known as Robin Hood and those who are said to have followed him.