They brought horses to England. This includes concepts of chivalry, knighthood and all forms of mounted warfare. Prior to that, the Britons, Saxons and Norsemen all over the country were foot soldiers.
They brought the French language in, which later merged with the Anglo-Saxon to give us all those English words that begin with "Ch".
They brought castles to England. The Normans were occupiers and so they needed fortresses to protect their newly-acquired lands in hostile territory.
They codified a system of taxation and geographic administrative divisions across England
They (eventually) brought a semblance of stability to England, which was in the 1000s overrun by Norsemen who were serious challengers to English sovereignty. They paved the way for the French nobility to enter Briton and bring England and Scotland into French politics, wars and institutions.