Here are a few (some of these are available in print only); they are all excellent.
Barbara Tuchman - "The Guns of August" about the first month of WW1 -
http://www.goodreads.com/book/show/1...Guns_of_August
Barbara Tuchman - "The Zimmermann Telegram" about one of the triggering events for the U.S. entry into WW1 -
http://www.goodreads.com/book/show/6...rmann_Telegram
Niall Ferguson - "The Pity of War" for a somewhat less conventional view of WW1 -
http://www.goodreads.com/book/show/1...he_Pity_of_War
Stanley Weintraub - "Long Day's Journey Into War" - gives the context of the worldwide conflict on the weekend of the Pearl Harbour attack -
http://www.goodreads.com/book/show/1...urney_Into_War
Stephen Ambrose - US bomber crews in WW2 (George McGovern flew a B-24) -
http://www.goodreads.com/book/show/487638.The_Wild_Blue
Elmer Bendiner - "The Fall of Fortresses" - some of the worst B-17 missions in WW2 by a participant - a great book but in print only -
http://www.amazon.com/Fall-Fortresse...7078386&sr=8-1
Modris Ecksteins - "The Rites of Spring" - the cultural impact of WW1 -
http://www.goodreads.com/book/show/1...tes_of_Spring_
Paul Fussell - "The Great War and Modern Memory" - the cultural impact of WW1 -
http://www.goodreads.com/book/show/1..._Modern_Memory
Paul Fussell - "Wartime" - the immediate impact of WW2 on participants - (Fussell was wounded in combat) -
http://www.goodreads.com/book/show/154474.Wartime
Personal experiences:
Robert Leckie "Helmet For My Pillow" - written by a WW2 marine -
http://www.goodreads.com/book/show/1...litary_History
Eugene Sledge - "With the Old Breed: At Peleliu and Okinawa" -
http://www.goodreads.com/book/show/7..._the_Old_Breed
William Manchester - "Goodbye Darkness" - Manchester was a U.S. Marine sergeant in WW2, the book is about his rememberances of the places where he fought as he visits them late in his life -
http://www.goodreads.com/book/show/1...odbye_Darkness
Henri Barbusse "Under Fire" - what life was like for ordinary French infantry in WW1 -
http://www.goodreads.com/book/show/48176.Under_Fire
Jaroslav Hasek - "The Good Soldier Svejk" - a satire about a Czech draftee in the Austr-Hungarian army on the Eastern Front in WW1 -
http://www.goodreads.com/book/show/7..._Soldier_Svejk
Many more here -
WW1 -
http://www.goodreads.com/list/show/1...terature#48176
WW2 -
http://www.goodreads.com/list/show/1...wo_Non_Fiction
and
http://www.goodreads.com/list/show/2...War_II_Fiction
Fiction -
The Richard Hannay novels about WW1 espionage are in the public domain - you can get them here -
http://www.gutenberg.org/ebooks/sear...oads&query=285
James Jones - "From Here To Eternity", "The Thin Red Line" - Jones was an infantry private in the Pacific before and during the war -
http://www.goodreads.com/author/show/3999.James_Jones