Some of my favorites are the openings to Batman: The Animated Series (which acts as a short story of its own!), DuckTales (with one of the catchiest melodies ever) and Alfred J. Kwak (which is both trippy but also heartwarming at the same time with an equally memorable melody to boot which sets the tone of the show perfectly). I guess I could also add the intros to Cowboy Bebop and Wolf's Rain into the list as well as both are atmospheric in different ways with great visuals.