There are very few good general survey texts of medieval warfare, so rather than recommend a couple of generic texts I'm going to suggest some specific books that may be interesting to you.

Maurice Keen's Medieval Warfare is still a decent introduction to a wide range of topics, even if it's beginning to show its age.

The magnum opus of medieval armour history is Alan Williams Knight and the Blast Furnace, but it's also an intimidating (and expensive!) place to start. For a more approachable book, Claude Blair's classic European Armour may be the place to go.

Ewart Oakeshott is your man for all things sword related. His Archaeology of Weapons is a fine place to start, but has its flaws. The Sword in the Age of Chivalry may be a better place to go if you want more sword-specific topics.

Jim Bradbury is great on wider topics in military history. His Siege Warfare and The Medieval Archer are among the best books on their respective subjects.

Michael Prestwich is excellent on all things Late Medieval England. His Armies and Warfare in the Fourteenth Century: The English Experience is one of the finest books on medieval military logistics I've ever read. The Three Edwards is an engaging look at how English warfare changed from Edward I to Edward III.

Anne Curry is a mus read if you're interested in late medieval warfare, particularly Agincourt. Her histories of that famous battle are the best around. I'm partial to here very approachable book Great Battles: Agincourt, but basically anything with her name on it is worth a look.

Kelly DeVries has written on so many topics it's hard to narrow him down to one recommendation. His Infantry Warfare in the Early Fourteenth Century has some great accounts of numerous battles. I've also heard good things about his biography of Joan of Arc, and his work on early gunpowder weapons is generally excellent.

If the longbow is your thing, the go to text is Strickland and Hardy's The Great Warbow. If you like crossbows...well you're going to have a harder time. Josef Alms European Crossbows is the best book around, but it's very out of print, while Payne-Gallwey's The Crossbow is very accessible but also 100+ years old.

If Carolingian/Merovingian warfare is your cup of tea, you might want to look into the writings of Bernard Bachrach. While not without his detractors, he's certainly written more on the subject than just about anyone else. It's not really my area, though, so I can't recommend any work specifically.

John France's Western Warfare in the Age of the Crusades: 1000-1300 is an often recommended history of a much broader type, but I must confess that I have yet to find the time to read it.

For specific conflicts I recommend the following:

Crusades: Thomas Asbridge The Crusades or Chris Tyerman's God's War

Wars of Edward I: I quite like Marc Morris' A Great and Terrible King for how it covers the financial impact of Edward I's conquest of Wales and wars in Scotland. For a broader sweep of the Scottish wars, The Three Edwards covers a lot of the main portions of the conflict. Maurice Keen's England in the Later Middle Ages is an oldie but a goodie as well.

100 Years War: David Green's The Hundred Years War: a People's History is an amazing account of the war's broader context. If you want a more militaristic approach, Anne Curry has a nice short history of the war.

Michael Howard's War in European History is a highly readable attempt at analysing the macro-evolution of western warfare, including the medieval period.

It's not comprehensive, nor exhaustive, but it does a decent job of explaining how medieval warfare differed from wars of later periods.