Commensalism is a type of symbiotic relationship where one species benefits and the other is neither helped nor harmed. The species that benefits may gain nutrients, support, locomotion, and protection from the host.
Barnacles on the skin of a whale.
Remoras swimming with sharks.
Cattle egrets and livestock.
Golden jackals following tigers.
Clownfish and sea anemone (considered as mutualism by some although the if the anemone benefits--it isn't well documented).
Viceroy and monarch.