Oddly enough, I've found that putting my infantry in loose formation when expecting a charge helps them better absorb the shock. Then, once the enemy horsemen are deep within my ranks, I order them to close their formation. Now the Horsemen are deprived of their best asset, their speed and mobility. If youre not willing to let your better troops take the brunt of this charge, I've also found that any unit that utilizes the "horde" formation takes the hit real well. So you may actually want to bring peasants for once as a human shield.