Beevor's book on D-Day is excellent, as are Stalingrad, Berlin and The Spanish Civil War
A few more I can recommend, some aviation, some naval, some military;
Reich Intruders by Martin Bowman - a history of 2 Group RAF during WW2
Dreadnought and Castles of Steel by Robert K. Massie - on the Edwardian naval arms race and the Great War at Sea, respectively
Firts Blitz by Neil Hanson - on the German bombing campaign against London in 1917-18
Engage the Enemy More Closely by Corelli Barnett - excellent overall history of the RN in WW2
The Price of Glory by Alistair Horne - brilliant short account of the Battle of Verdun
The Sea Warriors by Richard Woodman - history of RN frigates and other small vessels in the Napoleonic Wars and War of 1812
The Last Citadel by Noah Andre Trudeau - very detailed account of the operations culminating in the capture of Petersburg, VA, June 1864-April 1865
The White War by Mark Thompson - on the Italian Front in WW1
The Last Stand of the Tin Can Sailors by James D. Hornfischer - on the Battle of Samar
Pyrrhic Victory by Robert A. Doughty - operational and strategic account of the French Army in WW1
Culloden by James Prebble - short account of the last land battle on British soil
Caen; Anvil of Victory by Alexander McKee - very detailed and harrowing account of British and Commonwealth involvement in the Caen campaign from D-Day to Falaise
Cambrai 1917 by Bryn Hammond - account of the first large-scale use of tanks
Battle Cry of |Freedom by James B. McPherson - world-standard account of the American Civil War
I picked up Dresden by Frederick Taylor today, only two chapters in but it is promising to be brilliant. UK members, it's 3 quid in Tesco at the moment, well worth picking up