Small ship cruises in Europe that are not on a river or in the Mediterranean Sea are, by definition, European coastal cruises. Cruises along the Atlantic coast of Europe or the Norwegian fjords or in the Baltic or Black Seas would all fall into this group.
Many of these cruises stop at ports largely unfamiliar to Americans. How else are you going to visit Sevastapol (famous as a Soviet sub base and not far from the site of the "Charge of the Light Brigade") or Yalta (where Roosevelt, Stalin, and Churchill met at the end of WWII and the start of the Cold War). How many Americans have visited any city in Estonia or Latvia?
These are just a taste of the kind of adventures that await if you cruise this part of the world.
The Yachts of Seabourn - spend a lot of time in the Mediterranean but they also have some coastal cruises particularily in Northern Europe - Denmark, Norway, and Russia.
Hurtigruten - big emphasis on coastal Norway but has added itineraries throughout Europe.
Lindblad Expeditions - spends most of their time in the far flung regions of the world but the do cruise European coasts on a few occasions.
Voyages of Discovery - as they travel around the world, Voyages makes sure that they offer several itineraries focused on the United Kindom and Norway.
Swan Hellenic - more than most, Swan Hellenic can be called an English cruise line so they always include a few itineraries exploring the UK, Norway, and the Baltic.