If you're looking for WW2 history then anything that Stephen Ambrose did is top notch. To name a few: Citizen Soldiers, D-Day, even Band of Brothers which served as the inspiration for the HBO mini-series.
Also, although it's not about WW1 or WW2, Team of Rivals by Doris Goodwin is absolutely brilliant. It's about Abraham Lincoln's rise to the Presidency and how he made his cabinet from his political rivals. It's just a great, great book.