I'd like to recommend some really brilliant books. I don't know why I didn't do it before, it's such an obvious topic for a blog like this. All recommended books are mostly relevant to land warfare.
by James F. Dunnigan
Comment: A good beginner's book.
Edited by Franklin D. Margiotta
Comment: Should be #2 for beginners.
by Karl-Heinz Frieser
Comment: Extremely interesting and much-debunking German official military history work on the campaign in France 1940. Also available in German original, of course.
by Eike Middeldorf
Comment: A 1950's book. It's 90% great and 10% poor (too specific or still under impression of wartime misunderstandings). An OHL (Army GHQ) officer who was responsible for lessons learned in late WW2 summarizes both sides' tactics of the Eastern Front in WW2. It was most likely translated into English (I saw a claim that it was published in three foreign languages in an advert for it in the next book), but it's been out of print for decades.
by Eike Middeldorf
Comment: A 1950's book, full of gems. It describes the state of the art of German army know-how in the early 1950's, a mix of still fresh WW2 lessons, early nuclear war considerations and has some U.S. Army influences. The focus is on battalion to Kampfgruppe (~half brigade size) level. It was actually written with many co-authors. This book was probably translated into English once, but it's out of print, of course.
Gudmundsson's "On ..." series
Comment: Adequate description of the doctrinal evolution of the three branches in the 20th century.
"Roots of Strategy" series
Comment: Military classics, the quality of the volumes is declining. These military classics are available in their original languages as well, of course.
by Edward N. Luttwak
Comment: Necessary for understanding counter-intuitive dynamics in warfare.
by Stephen Biddle
Comment: The first few chapters are a very good read.
by Robert R. Leonhard
Comment: Very good review and debunking of some holy cows.
by Jim Storr
Comment: Storr attempts to lay a new foundation for military (land war) theory. I will write a full review of this book on this blog soon.
I suggest to read them in about this order. Most other famous books of the last two decades didn't impress me much. I learned nothing from reading "Breaking the Phalanx" or "The Utility of Force", for example.