It can be argued -- and has been -- that sieges and raids
were more typical of knightly warfare than battles or major campaigns.
Nonetheless, accounts of battles were as dramatic to readers in the Middle
Ages as they are today. Here is some of what is available on-line.
Historical Materials on Knighthood and Chivalry index
William of Malmesbury's 12th c. account of the Battle of Hastings (Internet Medieval Sourcebook).
The Battle of the Horns of Hattin, 1187 -- the disastrous defeat in Palestine that evoked the Third Crusade (Hillsdale College).
The long Memoirs of the Lord of Joinville were meant as a life of the saintly King Louis IX of France, but the author, the Sieur de Joinville, who accompanied him on crusade to Egypt, included a gripping account of the fighting (trans. Ethel Wedgwood; University of Virginia e-library).
Jean Froissart's accounts of the battles of Crecy, 1346 and Poitiers, 1356 (both at KCT) are among the most famous stories of the Hundred Years War. Much more about that war can be found at the Tales from Froissart site, including descriptions of sieges and raids.
Levy of Troops for Wars in Bohemia, 1422 -- a late medieval army briefly described (KCT)
Several accounts of the English Wars of the Roses can be found at the Hillsdale College military history site.