I hear a lot about them being these ultrapowerful invaders who always won. However, I've read many books, and have come across stories of the Vikings being defeated in parts of Spain, Italy, and Russia and not only not really confronting the Byzantines but serving in their militaries by choice.
I am familiar with the heavy colonization of Britain and Northern France, and am aware that Norman Vikings were invited by the Neapolitans to rule Southern Italy, but there doesn't seem to be a list on wikipedia of Viking defeats, and I'm sure there are some areas of the world where they were stopped.
One could mention the Battle of Edington, where Alfred the Great defeated a viking army. At the Battle of Chartres, the viking army under Rollo was defeated by frankish forces, after which the Treaty of Saint-Clair-sur-Epte was signed. More viking defeats happened at the Siege of Asselt and the Battle of Leuven, and arguably at Stamford Bridge.
There were certainly more defeats, but as many raids were small in scale, they are not remembered by history.