Up until recently, I had assumed that the heavy infantry and heavy cavalry on both sides would have been equipped with plate armor - breastplates and all that - because I assumed they'd been coming into use over the fourteenth century and therefore guys would have them. However, I read "The Medieval Warrior" by Mortin Dougherty, which includes an image of an English knight from the 1350's, who doesn't seem to be equipped with much plate beyond some leg and arm protection - his torso seems to be primarily protected by mail.
So, in the mid-fourteenth century, what would knights/heavy infantry/heavy cavalry have been wearing for protection? As well, how would this differ from generations of armor coming before and after?
at the time of Crecy (1346), plate armor was still in its infancy and very few knights or men-at-arms would have worn anything more than a coat of mail.
the earliest (mid 1200s) pieces of solid plate worn in medieval Europe were poleyns, which were small pieces worn to protect the knee. by the 1340s poleyns were smaller and more closely fitted, with large fan-shaped 'wings' that protected the sides of the knee.
couters were sometimes worn sewn onto the elbows of a mail hauberk. in the 1340s these would have been either individual pieces or attached to a primitive vambrace consisting of two hinged gutter-shaped plates wrapped around the forearm. plate besagews were sometimes attached to the armpit of a hauberk similarly to couters, but these were rare after around 1335, and disappear nearly completely after 1350. tubular upper and lower cannons (rerebrace and vambrace) joined by couters appear around this time (1330s).
beginning around 1310 schynbalds were worn to protect the front of the lower legs. these were also called demi-greaves, and by the second quarter of the 14th century you do see full greaves that protected the entire lower leg.
both mail gauntlets and sabatons were often reinforced by overlapping horizontal plates called lames. by the 1340s these lames had become larger and fewer in number. not until the 1350s would the famous "hourglass" style of a single curved plate covering the back and sides of the hand come into use.
thigh armor called cuisses were not made of plate steel until well into the second half of the century, but after ~1320 it was possible that some knights wore plate cuisses made of cuir bouilli. also, after about 1340, some gamboised cuisses (quilted, knee-length cloth leggings worn under or over mail chausses) incorporated small riveted strips of metal.
some knights may have worn a coat-of-plates or a brigandine, which were poncho-like cloth garments lined with small metal plates, but these were not as common as the more popular mail hauberk*. plate cuirasses were not widely used until after around 1350.
*see u/WARitter's comment below