Anything by Cornelius Ryan (The Longest Day, A Bridge Too Far, The Last Battle) or Stephen Ambrose (Band of Brothers, D-Day, Citizen Soldiers) is good. John Keegan is a favorite of mine, but his scope is all of military history. A cool fact/trivia book is Dirty Little Secrets of World War II by James Dunnegin
When I was in my "German planes are cool phase" as a kid, I read Stuka Pilot, (Rudel) and The Luftwaffe War Diaries,(Bekker.)