Websites such as Rotten Tomatoes, IMDb, Movie Insider and Metacritic have lists of many years' top movies. Rotten Tomatoes has lists of every years' most popular movies since 1950.
Magazines and newspapers are also good resources for finding a year's top movies. The New York Times, Time Magazine and The Guardian all publish lists of film recommendations.
Some of the most popular films of 2015 include Avengers: Age of Ultron, Jurassic World, Mad Max: Fury Road, Furious 7, Tommorowland, Ex Machina and Fifty Shades of Grey. Wikipedia also has a page dedicated to listing the highest-grossing films of all time.