For science fiction fans, The Three Body Problem, The Dark Forest, and Death's End, a trilogy by Cixen Liu that's really interesting.
For history fans, George Marshall, by David Roll is one of the best books I've read in a long time. You really get an appreciation of what a great man Marshall was, and how well he served this country.
Zara Steiner's The Triumph of the Dark explores the years between WWI and WWII, and there's lots of information that wasn't touched on in other books on the topic I've read. Steiner passed away this year, and I believe this was her last book. The analysis and how she brings this material to life are astoundingly good.
The Wages of Destruction, by Adam Tooze, explores what happened in Germany economically during WWII and leading up to it. The emphasis is on the economic issues that doomed them from the 1930s throughout the arms buildup and the subsequent war, and mismanagement of whatever economic opportunities they might have had after the conquest of France in 1940. It's a real eye-opener to a subject matter that's rarely discussed by historians. It explains a lot. Not everything, but a lot.
Klaus Mann's classic book Alexander is a semi fictional work about Alexander the Great. Alexander is always an interesting subject. Klaus Mann was the son of Thomas Mann, who fled Germany before the war and wound up an American citizen. Klaus served in the US Army, but was himself an author who wrote in a German style.
Speaking of classic books by German authors, if you've never read it before, Hermann Hesse's The Glass Bead Game is an amazing tale that raises interesting philosophical questions, but it's also a wonderfully entertaining read. Hesse was also the author of Siddhartha, a book every hippie was required by the Law of Hipness to read in the '60s, but he was far from a hippie. Think of him as the intellectual counterweight to Vonnegut, both using the novel to comment on the weirdness of the world. I read this in college (yes my college was in a cave and the material was taught by shamans, but it was all we had), and re-read it this year.
Richard Miles' Carthage Must Be Destroyed explores the Punic Wars that kicked off the era of Roman power in the Mediterranean. I wish they'd titled it Carthago Delenda Est, the famous Latin phrase every high school Latin student translates from the speech made by Cato the Censor that means the same thing Oh well. Cato probably said Ceterum autem censeo Carthaginem esse delendam, anyway, but students are taught the shorter phrase in Latin 2. Regardless, it's an interesting read.
If you like a little philosophy along with your intellectual history, there's no better read than The Age of Genius, by A.C. Grayling. It's about the science developed in the 17th Century that got the modern era going. We don't think about the 17th Century much, but it started with Galileo and culminated in Sir Isaac Newton. Pretty important era. Grayling is a terrific writer, and brings the history to life.
Empires of the Sea includes the battles of Malta, Lepanto, and others for control of the mediterranean between Western European states and the Turkish Empire in the 1500s; it's pretty engrossing stuff. Roger Crowley is an excellent historian, and a good writer.
For those interested in Civil War history, Memoirs of Ulysses S. Grant is the most detailed analysis of the battles he led and of his career during the period from the Mexican war through the Civil War. Turns out Grant was an excellent writer! I expected flowery 19th Century prose. Nope. It's a very modern read, and it's actually pretty exciting, if you like military history. It's also interesting to read a book by the person who lived it, as opposed to a person studying it a century and a half later.
If you've never read Churchill's series of histories of his WWII experiences, the man was a great writer - in fact, he was published beginning in the late 19th Century, was a war correspondent himself (Boer War) and had already written a very good book on Marlborough, his ancestor, before the war. There's a lot of Churchill being egocentric Churchill in this series, but again, it's history by the person who lived it, instead of history one or two generations removed from events.